A Blog About Stone Gathering, Tumbling and Polishing, and Rocks and Landscapes, from New Zealand – With Musical Interludes (john.tumblestone@gmail.com)
The purpose of this and the following Posts is to examine how the 40 Riverton stones have emerged from the polishing process and to compare them with how they looked before polishing. The Seven Stages that these 40 stones have gone through are: Stage One, Stone Collection; Stage Two, Silicon Carbide 100 Grit Tumble; Stage Three, 220 Grit Tumble; Stage Four, 320 Grit Tumble; Stage Five, Tin Oxide Pre-Polish; Stage Six, Pro-Polish; and Stage Seven, Borax Burnishing.
This is the 12th Post in this series – the first Post can be found here.
To start with Stones 1 to 5 [Note: The second photo below does not do justice to the shine on the polished stones, due to the artificial lighting conditions under which the photo was taken]:
Stones 1 to 5, rough, as collectedStones 1 to 5, after polishing
STONE 1
Before polishing, Stone 1 (far left) was about 8 cms long and about 5 cms wide at its widest point (using the graph paper under it) and after polishing it has lost perhaps only a few mms of size. I had noted in Post Two of this series that Stone 1 is most likely of volcanic origin, probably rhyolite, as it has small specks in it that would have originally be gaseous pockets. [Note: I have since decided that this stone is ignimbrite, not rhyolite.] After the 100 grit tumble, these small pits were obvious. I noted after both the 220 grit tumble and 320 grit tumble that further wearing away of the stone did not do away with these pits. They would prevent the stone from achieving a smooth polish over all its surface. Further tumbling in 320 grit would not have solved this problem. I have previously (and since) tumbled the same type of stone where the gaseous pockets appear to have been filled in with material and they have been very successfully polished over all their surface.
Stone 1 has polished well except for the many gaseous pits to be found across its surface. Close inspection with my magnifying glass also revealed some small cracks that had not been worn away and which I had not previously noticed:
Stone 1 polished
Stone 1 polished
Stone 1 is covered in small pits that have not polished.
Small pits on the surface of Stone 1
In the centre of this photo, a small crack is apparent
This stone is in contrast to other rhyolites [ignimbrites] I have tumbled, where the gaseous pits have not been void:
Stone 1 is well-patterned and a nice large size. Even though it has failed to polish completely, it remains a fine specimen. The tumbling has brought out its pattern clearly.
STONE 2
Stone 2 is similar to Stone 1 in that it is of volcanic origin [probably rhyolite] and also started out with noticeable gaseous pits the size of which was actually a little larger than Stone 1. However, most of these pits were filled with material which resisted crumbling and which polished quite well. In general, Stone 2 polished much better than Stone 1. However, there are a small number of pits which did not polish and two small cracks that are apparent.
Stone 2 after polishing
Stone 2 after polishing
A pit that crumbled and did not polish
Another pit
Two cracks that had not been removed by tumbling
When rubbing a thumb across one side, a couple of these indentations are noticeable and interrupt the smoothness. Another tumble in 220 grit would probably have removed most of the pits and cracks, although there is no guarantee that all of them would have disappeared.
STONE 3
Stone 3 looks like a mudstone that has undergone metamorphic pressure. It is fine-grained and has lovely green patches and swirls. From the beginning it seemed free of pits and cracks and had polished very well. The beautiful patterns discernible in the rough stone have been revealed and clarified.
Stone 3 after polishing
Stone 3 after polishing
Close-up of a polished Stone 3
Close up of a polished Stone 3
There is just a slight roughness along one edge, not very noticeable really, but otherwise it is excellent.
STONE 4
It was noted during the inspection of Stone 4 after the 100 grit tumble that it had a small indentation in it. I would normally have tumbled it again in 100 grit, although there is always the risk that this might reveal other soft spots. After the 320 grit tumble, I saw that the indentation had smoothed out a lot and thought that it might not affect the final polish. At the end of the polishing process, Stone 4 has turned out very well.
The polished Stone 4
Stone 4 after polishing
Detal of Stone 4 after polishing
Partially smoothed out indentation
Area of partially smoothed out indentation
This stone is a breccia, composed of broken angular fragments of rock cemented together in a fine-grained matrix. Sometimes indentations in such stones are caused by a softer fragment being worn away more quickly than the rest of the stone. This is not the case here – the indentation is maybe a less compressed part of the matrix. It has polished to a significant extent but can still be felt when a thumb is rubbed over the surface of the stone. The only other notable thing is that the very edge of the point half way down the stone is slightly rough – another 320 grit tumble would have smoothed this out.
STONE 5
This stone has polished very well. It feels smooth all over. The eye can vaguely discern a few very small pits along one side which can be confirmed with a 3x magnifying glass. But these do not detract from the overall smoothness.
Stone 5 after polishing
Stone 5 after polishing
Close-up detail of Stone 5
Stone 5 looks at first glance to be a metamorphic mudstone or sandstone but closer inspection shows it to include lots of small pieces of different things, including pits (filled in) that are normally found in a volcanic stone. Many of the stones I find cannot easily be identified by me.
(This is the 11th Post in this series – the first Post can be found here.)
Steve Hart, in “Modern Rock Tumbling” (2008), attests that burnishing can make a “significant difference” in the appearance of polished stones (page 44). As one tumble-polisher has put it, “Sometimes stones are a little ‘hazy’ when they come out of the polish and small particles of polish are hidden in the tiny crevices of the stones. It helps to clean them up by burnishing the rocks in soapy water for 4-5 days.”
It was while I was doing my initial internet searches on how people tumble polished stones that I came across the idea of a post-polish burnishing tumble for up to a week using borax. Borax is sold as a white powder that dissolves easily in water. It has been used as a detergent, a food preservative (now banned for this use in some countries), an anti-fungal compound, a weed killer and a low-toxicity insecticide. It is used by tumble-polishers because it is a clean soap, lacking perfume and other additives (some use Sunlight or Ivory soap flakes instead). So I tried it and I thought that the results were great – polished stones seem to sparkle just a little more. Whether this is the case or not, I am not entirely sure, but I have the attitude that if it seems to work, why not continue it! In general, I think that a soap tumble of newly-polished stones for a day is the least that should be done, to remove polish particles and to give a final clean. My established routine practice is a tumble for around one week in one to two tablespoons of borax.[NOTE: April 2021 – I now do a borax tumble for an average of two days and the results still seem to be good.]
I polished the 40 Riverton stones, that this series is about, in borax for 10 days straight after the pro-polish tumble. This was a little longer than usual as I was busy with other things over this period. Firstly, the washed stones and pro-polish beads were replaced in the 4lb barrel, with water, and then about two tablespoons of borax were added.
Two tablespoons of borax in the 4lb barrel in which the stones and plastic beads have been placed, topped by water.
At the end of the tumble, the stones were washed then given a final weighing:
The starting weight of the unpolished stones, right before I began to work with them, was 1605 grams, the end weight is 1244 grams. This means that 361 grams were worn away during the whole polishing process, which is 22.5%, just over one-fifth, of the stone material.
SUMMARY OF TUMBLING STAGES AND TIMES (as taken from Tumbling Log)
(Stage 1 = Stone collection)
Stage 2, 100 grit = 9 days 10 1/2 hours, followed by soap tumble of 12 hours
Stage 3, 220 grit = 9 days 2 hours, followed by soap tumble of 18 hours
Stage 4, 320 grit = 9 days 19 1/2 hours, followed by soap tumble of 3 days 1 1/2 hours
Stage 5, Pre-polish = 5 days 19 hours, followed by soap tumble of 20 hours
Stage 6, Pro-polish = 14 days 5 hours
Stage 7, Borax = 10 days 2 hours
This adds up to the stones spending 49 days and 8 hours tumbling in grit and polish, with an additional 15 days and 5 1/2 hours spent tumbling in soap and borax (a total of 64 days and 13 1/2 hours). Note that this is not the minimum time needed – I often extended tumbling by a day or two in some Stages, and there were occasions where tumbling in soap went on far longer than usual. Furthermore, a smooth beach stone can usually skip Stages One and Two.
The following Posts in this series look at each of the polished stones in detail to assess the impact of this process on them. The first examines Stones 1 to 5.
NOTE: March 2021. My supplier now stocks only one grade of tin oxide polish powder instead of two. This means that Stages Five and Six can be replaced with one stage. Details can be found in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage. I will leave the original Posts unchanged as the detailed activities of either Stage can be applied directly to the use of one polish stage.
(This is the tenth Post in this series – the first Post can be found here. Apologies for the delay that’s interrupted this series.)
In his book, “Modern Rock Tumbling” (2013), Steve Hart, a mechanical engineer, comments that how a stone becomes shiny after polishing is both a miracle and a mystery:
There is no one who really knows what happens inside the barrel when polish is added to the rocks. The Silicon Carbide stages were relatively easy to understand, because the process was primarily mechanical erosion or abrasion. Not so with polish. There are “mysteries” that don’t add up… There are theories that a given polish may liquefy the top layers of molecules on the rocks and rearrange them so the surface is smoother. Others say it may be an acid/base pH thing, or perhaps a frictional heat buildup phenomenon which causes the rock surface to flow… Another theory is that the rock surface is simply mechanically hammered… down to a smoother condition… After really trying to understand the polish process, I had to give up, because no one… really knows what’s going on (pages 40-41).
Stage Five of tumble polishing used a “pre-polish” tin oxide powder of five micron size. Stage Six uses a “pro-polish” tin oxide powder of one micron size. In general terms, I am following the instructions provided by Colin Simmons of the Rotorua Rock and Gemstone Shop from whom I bought my tumblers. He also sells the two grades of tin oxide powder. Colin recommends that the Pro-Polish tumble should be for at least seven days, and he states that the pro-polish mixture is retainable and reusable for about six batches of tumbling as long as it does not become contaminated. In this instance, I used a pro-polish mix that I had used five times before.
The procedure for starting the Pro-Polish tumble is the same as for the Pre-Polish stage, using the key ingredients: the 4lb tumbler, the white pro-polish tin oxide powder, a plastic shaker with a tight lid, and the plastic beads kept for pro-polish tumbling (see the relevant previous Post for details):
I try to tumble a pro-polish batch for at least 10 days, even though Colin Simmons states that it is okay to tumble for only seven days (as the minimum). In this case, I had taken on a temporary job which kept me busy while the stones were tumbling and I left them for a total of 14 days and five hours before taking the barrel off the machine. The process of taking the stones out of the barrel and washing them is the same as detailed for the Pre-Polish Stage(Note, January 2022 – I have just come across an observation from an experienced polisher that using a metal colander to rinse stones at the polish stage tends to put metallic streaks on the stones. I have not noticed the same issue with a metal sieve):
I then use my pro-polish toothbrush to finish cleaning the barrel before the next stage:
However, instead of then putting the stones in a soap tumble, they undergo a longer tumble wash in borax as a burnishing process, which is Stage Seven, described in the next Post in this series.
(This is the ninth Post in this series – the first Post can be found here.)
Two of the stones have suffered some minor damage in the Pre-Polish tumble, probably from bumping into other stones. This is despite careful handling and the use of plastic beads to cushion collisions in the barrel. This will happen from time to time due to the brittle make-up of some stones. Stone 6 has lost a small chip in its side:
Stone 12 has has lost three or four small pieces, the largest being apparent in the photo below:
In such cases, stones are usually returned to Stage Two or Three, to be re-tumbled with 220 or 320 grit to get rid of the pits. However, I will put them through to the Pro-Polish stage for the sake of this series of Posts.
The following are the stones as they looked upon initial collection from the beach at Riverton and then upon completion of Stage Five, Pre-Polish. In both instances, the stones are dry. Note that the same sized segment of graph paper is provided in these comparative photos. At present the stones look a lot smoother and shinier, and are slightly smaller. Their colours are clearer and brighter, with any patterns being more obvious.
Stones 1 to 5:
Stones 6 to 10:
The grain of Stone 6 is now apparent. The wearing away of Stone 7 has led to the band across its lower part to be uncovered more and thus made to appear larger.
Stones 11 to 15:
Stone 12 now has a depth to it as parts of it are translucent.
Stones 16 to 20:
Stones 21 to 25:
Stones 26 to 30:
Stones 31 to 35:
Stones 36 to 40:
The next step is Stage Six, the Pro-Polish tumble.
NOTE: March 2021. My supplier now stocks only one grade of tin oxide polish powder instead of two. This means that Stages Five and Six can be replaced with one stage. Details can be found in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage. I will leave the original Posts unchanged as the detailed activities of either Stage can be applied directly to the use of one polish stage.
(This is the eighth Post in this series – the first Post can be found here.)
Stages Two, Three and Four tumble the stones in different grades of silicon carbide grit, shaping and smoothing them, ready for the two polishing stages. I use two different grades of tin oxide for my polishing – others use a very fine silicon carbide grit (e.g., 600 grade), sometimes skipping the 320 grit tumble stage, followed by only one polish-tumble with a powder such as tin oxide, aluminium oxide, cerium oxide, or chrome oxide.
I am following the stages set down in the Instructions provided by Colin Simmons of the Rotorua Rock and Gemstone Shop when I bought my tumblers. He also sells tin oxide powder, which is why I use it – it is the cheapest polish powder. The “Pre-Polish” stage uses powder of a five micron size while the “Pro-Polish” stage uses powder of one micron size. “Pre” and “Pro” look very similar so you have to be extra careful when labelling containers, sieves, beads etc. and when using them.
Colin Simmons recommends that the Pre-Polish tumble should be for three to five days, which is shorter than the other tumble stages (which should be for at least seven days), and he states that the pre-polish mixture is retainable and reusable for about six batches of tumbling as long as it does not become contaminated.
Stage Five begins with gathering together the key ingredients: the 4lb tumbler, the white pre-polish tin oxide powder, a plastic shaker with a tight lid, and the plastic beads kept for the pre-polish tumbling:
The 40 stones are then carefully placed into the barrel – care is taken to avoid chipping them. After the first layer of stones, I add a layer of plastic beads, just to make sure the stones are cushioned from the outset when tumbling starts:
Adding some plastic beads after the first layer of stones in the barrel.
After all the stones are in the barrel, I use plastic beads to fill the barrel up to about the two-thirds level (more beads are needed at this than at earlier stages as the stones are now smaller than when they started):
The barrel two-thirds full with stones and beads.
The next job is to add the pre-polish mixture. Often a previously used mix will be available. In this case, I created a new mix from the start. Following Colin Simmons’ Instructions, I place nine tablespoons of tin oxide pre-polish powder into the shaker:
Adding tin pre-polish powder to the shaker.
The shaker is half-filled with water, the lid screwed on tightly, and the mixture is given a good shake (over the sink in case of leaks). I have found this to be the best way to mix up both pre-polish and pro-polish, having one shaker for pre-polish and one for pro-polish to avoid contamination:
The result of shaking the powder and water to mix them. The powder settles quite quickly so the mix needs to be poured into the barrel very soon after it is ready.
Colin Simmons states in his Instructions sheet that the resulting mix should have “the consistency of household paint”. I pour that into the barrel until it just covers the stones and the beads are floating:
The top can then be placed on the barrel and it can be put to tumbling:
As always, I record all of this in my tumbling log:
I try to tumble a pre-polish batch for a period of between five and seven days, even though Colin Simmons states that it is okay to tumble only for three days (as the minimum). In this case, I took the barrel off the machine in just under six days (five days 19 hours to be exact). I place the pre-polish shaker in a large shallow blue plastic bucket with the sieve over it (Note, January 2022 – I have just come across a suggestion from an experienced polisher that it is better using a plastic colander or sieve, not a metal one, to rinse stones at the polish stage as the metal ones tend to put metallic streaks on the stones. I am considering making this change):
I clean the blue plastic bucket before use in case I need to pour off any spillage back into the container. When the contents of the pre-polish tumble are poured into the sieve, it can be difficult to direct the liquid into the shaker container, which is why I don’t use the plastic “safety” colander for this. A plastic sieve may be better than a metal one for this.
Opening the barrel, I pour the contents into the sieve, allowing the pre-polish mix itself to drain into the shaker. Most of the liquid will end up in the shaker but if too much gets away, into the bottom of the bucket, then the bucket may need to be tipped up to pour it into the shaker:
I note on the shaker the date when the mixture was used. The pre-polish powder eventually settles at the bottom of the shaker. The mix can be re-shaken and used again, at least five or six times:
I then place the sieve over my usual red bucket and wash the stones and beads with fresh water and put them back into the tumbler barrel for a soap tumble:
I use a small sieve (or my fingers) to recover any stray plastic beads that have escaped into the bucket, before discarding the water:
Once all the stones and beads are back in the barrel, I add water and a few gratings of sunlight soap, put the top on, and then start the barrel tumbling again. This washes both the stones and the barrel in preparation for the next stage, to avoid contamination:
I usually do a soap tumble for at least three hours, maybe as long as a day. In this case, I ran the soap tumble for just under 20 hours:
I wash the soapy water from the stones and plastic beads:
The water is a grey colour afterwards, and there are more escaped beads to recover:
I place the stones on a paper towel to dry prior to inspection and sorting in preparation for the pro-polish stage. They now retain a shine even when not wet:
I complete the tumbling log entry, adding the time for the soap tumbling. This brings Stage Five to completion. The next Post looks a little more closely at the stones at this Stage, comparing them with how they looked when collected.
This is the seventh Post in this series – the first one can be found here. This current Post concerns a process that occurs after Stage Four and prior to Stage Five.
After the stones have gone through Stage Four, being tumbled with 320 grit, they are a lot smoother than previously. Normally I would inspect each stone for any “imperfections” before putting them through the final two polishing stages. This involves looking at each dry stone under a bright light, sometimes with the aid of a magnifying glass. Those stones that fail this inspection would be tumbled again in 220 or 320 grit to remove the “imperfections”. However, for the sake of this series of posts, I am going to put all 40 stones straight through to the polishing stages. The following ten stones are ones that I would normally consider holding back at this stage.
Stone 31, one of the smaller stones, is in the worst condition, with a number of gouges, pits and indentations. The stone is probably made of brittle material which predisposes it to lose parts even during the tumbling process. Usually I would discard this stone altogether.
Side of Stone 31 after 320 grit
One end of Stone 31 after 320 grit
Other end of Stone 31 after 320 grit
Stone 11 initially had a very minor superficial crack which had been smoothed out more and more during the tumbling process. However, after the 320 grit tumble, there is still about 1 mm of the crack remaining. I would usually give this stone another tumble in 320 grit before going on to the next Stage.
Stone 11 after 320 grit
Remnant of superficial crack on Stone 11 after 320 grit
Stone 19 still has a small section of crack apparent, and another small crack has appeared as a result of the 320 grit tumble. These are likely to be at least partly due to the patterning on the stone, of the white streaks throughout the grey rock. Further tumbling in grit is likely to smooth out one or both cracks but create others. It is worth putting this stone through to the next Stage to see how it emerges from the polishing process, mainly because of its interesting pattern.
Stone 19 after 320 grit tumble
Two very small cracks apparent on Stone 19
I noted after its tumble in 220 grit that Stone 1 has a number of small pits that arise because it is a stone of volcanic origin with small gaseous pockets. Tumbling the stone reveals and exposes more such pockets. This is apparent also after the 320 grit tumble. It is always hard to judge whether further tumbling in 320 grit will improve its smoothness or simply reveal more gaseous pockets.
Stone 1 after 320 grit tumble.
One of the small pits still apparent in Stone 1
The small gouge in the side of Stone 15 has been further reduced by the 320 grit tumble, but remains larger than I would normally like at this stage.
Stone 15 after 320 grit
The small gouge in the side of Stone 15
The surface crack on Stone 20 has been significantly reduced by the 320 grit tumble but requires this to be repeated as it still catches a fingernail crossing over it.
Stone 20 after 320 grit
Surface crack on Stone 20
Stone 9 has a pit in its side, which has been smoothed out further by the 320 grit tumble. This indentation could be made up of softer material that the surrounding rock so it may continue to erode faster if re-tumbled in grit.
Stone 9 after 320 grit tumble
Side of Stone 9
Stone 10 still has its deep pit, and a couple more small pits have also appeared. This stone could be discarded.
Stone 10 after 320 grit
Deep pit in Stone 10
The indentation in Stone 4 has smoothed out further and it is possible that this might not affect its final polish.
Stone 4 after 320 grit
Indentation in Stone 4
Finally, small cracks in Stone 25 still remain but are very small.
Stone 25 after 320 grit
Small crack in Stone 25
The next step is to tumble all 40 stones in Pre-Polish mixture – see the eighth Post in this series.
In order to develop the polish or shine on a stone, the stages of smoothing using grit need to be followed up with one or two tumbles with polish. There are a number of different materials that can be used for polishing. These tend to be much more expensive than grit but can be reused for a number of tumbles. In 2018, I used two grades of tin oxide (“pre-polish” and “pro-polish”) because that was what was recommended to me when I bought my first tumbler, it was easily available for purchase, and it did the job very well for me. In March 2022, Rotorua Lapidary stock only one grade of what they call “Tumble Polish” (which is actually aluminium oxide) priced as follows: 250 grams = NZ$14.40, 500 grams = NZ$23.20 and 1 kg = NZ$40.80. (Colin Simmons has advised me that “with using 400 grit, which is finer, instead of 320 grit you can eliminate the pre polish process” He had trialed the use of 400 grit and the new Tumble Polish and had full confidence in it.)Mr Grit also sells aluminium oxide polish powder.
Colin Simmons had recommended that 7 tablespoons of pre-polish and pro-polish be used for each 3lb barrel load and 9 tablespoons for each 4 lb barrel load. I had followed these suggestions successfully in my own tumbling. I will continue to use these amounts of the new “Tumble Polish”. Each lot of polish mix can be re-used up to six times (because it takes longer to lose its effect, and it does not wear away the stones and thus get contaminated as grit does, though contamination can sometimes occur).
SAY you buy 500 grams of Tumble Polish = NZ$23.20 (plus postage)
TOTAL so far = NZ$598.15 (plus postage)
7) POLISH POWDER STORAGE AND TABLESPOON MEASURING, AND POLISH MIXING AND STORAGE
I store my polish powders in plastic containers with tight lids (see photo below – note that with only one grade of polish powder, only one plastic container is needed). I also have one measuring spoon per container and keep it exclusively in the same container. Again you could simply use the same metal tablespoon as used for the grit as long as it is cleaned after each use, or dedicate a separate metal spoon for the polish powder.
The polish powder needs to be mixed with water before being put into the tumbler barrel with stones. For months I struggled to find a way of doing this without messes, leakages and spills. I also had difficulty finding a way to store mixtures after use in such a way that re-mixing could easily be done (as the powder settles at the bottom of the water after a short time). The best solution I have come up with is a plastic shaker with a very tight lid. I again use a Sistema product, a700 ml To Go Shaker, costing about NZ$8 each, as other shakers I tried of a similar cost tended to leak when shaken.
SAY you buy one powder storage container for NZ$13, one tablespoon measuring spoon for NZ$5, and one shaker for NZ$8 = NZ$26
TOTAL so far = NZ$624.15 (plus postage)
The two storage containers for pre-polish and pro-polish powders. NOTE – only one needed now.
The two shakers for the mixing and storage of pre-polish and pro-polish. Note how the tin oxide settles on the bottom of the containers. Excess water can be poured off before re-mixing and use. NOTE: Only one needed now.
8) PLASTIC BEADS, BEAD STORAGE AND SPOONS
Plastic beads (or pellets) are added to stones in tumblers to cushion loads (so the stones hit each other less to avoid chipping etc.), to top up batches to the 2/3 mark of the barrel if needed, and to carry the grit and polish to all parts of a stone. [I am now exploring options to the use of plastic for these purposes – Mr Grit sells ceramic media, one alternative. See my Post “Alternatives to Plastic Pellets as Tumbling Media: Reviewing the Advice”.] The amount needed per barrel varies on the number of stones used, and tends to be greater as you move through the various stages of tumbling. I usually put 1 to 2tablespoons in a tumbler even if I have enough stones to fill it to the 2/3 mark. The beads are long-wearing and reusable. They are worn away only very slowly, over years, during the tumbling, but can be contaminated by the different grit grades. So you don’t need a lot per batch but it can be useful to keep separate the beads used for the different grits and polishes.
Colin Simmons of Rotorua Lapidary sells plastic beads (pellets) in the following lots –in March 2022, 500 grams for NZ$13.80, and 1 kg for NZ$24.50. I store the beads used for the various stages in separate 1 litre plastic containers (I used to use Sistema ones but they changed the design and the lids are tighter fitting making them harder to use, so I now use ones made by Visto that cost NZ$3.50 each). I have two metal tablespoons for use with the beads – one set aside for the three grits and one for the polish. I use these to ladle the beads from the storage container to the barrel, and to ladle the used beads from the sieve back to the storage container after each load. They live in two glass jars.
SAY you buy 1 kg of plastic beads for NZ$24.50 (plus postage), four 1 litre bead storage containers (NZ$14.00) and two metal tablespoons (NZ$3.00) = NZ$41.50 (plus postage)
TOTAL so far = NZ$665.65 (plus postage)
Beads for different Stages in their separate containers.
9) SOAP FOR CLEANING AND BURNISHING
It is a good idea to do a soap tumble for between two hours and one day after each tumble stage. This gets rid of any minute amounts of slurry or grit or polish from the stones and barrel. The test of the effectiveness of this is the dirty colour of the water afterwards. The type of soap that should be used should be mild, non-perfumed and as pure (free of additives) as possible. I use sunlight soap(as I saw it was sometimes recommended by tumblers) – I buy three bars (I think it is) for NZ$4.00. I grate the bars and store the soap in a plastic container, adding just a few gratings to a washed batch of stones after each tumble.
After the final pro-polish tumble, it is recommended by many that a “burnishing” tumble be done which will make the stones just that little more shinier. My experience has proved this correct. I read somewhere sometime that someone used borax soap to do this, with good results. Borax can be hard to find – I usethis product, priced at NZ$10.90 for 1 kg (I have also purchased a bulk amount for much less off Trade Me). I add about 1 to 1 1/2 tablespoons in a 3lb barrel and tumble for at least 3 days, sometimes up to a week. [An alternative to Borax can also be used, again a soap that is mild, non-perfumed and as pure as possible.]
SAY you buy sunlight soap (NZ$4.00) and borax (NZ$10.90), and a small plastic container for sunlight soap gratings (NZ$3.50) = NZ$18.40
TOTAL so far = NZ$684.05 (plus postage)
Container of grated Sunlight soap and two whole bars as well.
10) SIEVES AND BUCKETS
In order to wash a batch of stones and beads after each tumble, I use astainless steel sieve, costing around NZ$5, with a larger plastic colander beneath it (one like would be suitable) costing around NZ$3, with a plastic bucket under them. I run water over the stones and beads to clean them and wash the slurry off them. The stainless steel sieve retains the stones and beads as the water runs over and through them, the larger plastic colander acts as a safety net in case stones or beads getwashed out of the stainless steel sieve (so they are easily retrievable), and the bucket holds the slurry to be disposed of safely afterwards.
I often use a second bucket to place the sieves on while I dispose of the slurry in a slurry storage bucket, wash out the original bucket, then place the sieves back on the original bucket to wash the stones and beads again – the resulting water is not very dirty and can be disposed of on the ground outside or elsewhere, keeping the level in the slurry storage buckets to a minimum. I would recommend that you use at least two stainless steel sieves, one for the grits and one for the polish, with thorough cleaning in-between tumbles. However, to avoid contamination across grits, I decided to have a stainless steel sieve for each grit grade and polish powder.
SAY you buy two stainless steel sieves (NZ$10.00), one plastic colander (NZ$3.00), and two 10 litre plastic buckets (NZ$10.00) = NZ$23.00
TOTAL so far = NZ$707.05 (plus postage)
Stainless steel sieves for each Stage of tumbling.
My larger plastic colander.
11) MISCELLANEOUS USEFUL ITEMS
First, a “tumbling log” is important, even if it is only a piece of paper kept near your tumbler. You need to write down for each batch of stones you tumble things like: the type of stones, where the stones came from, the grit or polish grade used, when tumbling started (so you know when to stop), and anything unusual about the batch. Secondly, I use paper towels a lot, to dry stones, clean barrels, wipe down surfaces and so on. If a cloth were used, there is the problem of potential contamination. Thirdly, I use old toothbrushes to clean the parts of the barrels that the lid rests on, to help ensure a clean fit – I have one toothbrush per grit and polish (five toothbrushes in all) and keep them in a glass jar. Fourthly, I use a permanent marker pen to write things on storage jars etc, so I know what is in them (using methylated spirits to remove the writing when needed).
SAY you buypaper towels (NZ$5.00) and a marker pen (NZ$4.00) = NZ$9.00
GRAND TOTAL = NZ$716.05 (plus postage if buy tumbler, grit, polish and beads online)
Glass jars for spoons for beads and old toothbrushes for cleaning barrels – for grit on the left, for polish on the right.
Occasionally I get asked these questions by someone who is considering polishing their own stones. The answer is not simple. The following account aims to be fairly thorough and realistic. Another of my key considerations is the use of equipment and processes to avoid the cross-contamination of tumble grits which can spoil the polishing process. As a tumbler manufacturer puts it, “Contamination is the primary reason for inferior results” (from Lortone’s booklet, “Professional Gemstone Tumbling”). Keep in mind, too, that some of the things bought at the beginning will be useful for many weeks, if not months or years. [For more information on tumble polishing in general, see “Tumble Polishing” in TumbleStoneTwo.]
This is my attempt to set out what a beginning tumble polisher needs and how much it will cost (the costs reflect that I live in New Zealand and for 2018 – up-dated March 2022 prices for tumblers and grit are in light green below, with 2021 prices for other material also in light green below):
1) TUMBLER
First of all, a tumbler is needed. My tumblers are of the “rotary” type by Lortone (a US manufacturer) and I have found them to be excellent. There are not many others available in our part of the world. NOTE: In October 2024, a new seller of lapidary equipment and grit appeared in New Zealand, Mr Grit.Based in Christchurch, Luke Schmidt has started to import equipment and polishing materials from Australia. The New Zealand Lortone dealer is the Rotorua Rock and Gemstone Shop (1120 Eruera Street, Rotorua, owned by Colin and Bev Simmons) which has a selection of tumbler sizes for sale. The smallest size is Model 3A, a single 3lb barrel, also the cheapest (NZ$249 in 2018 $319.40 in March 2022). About 45 to 55 small stones (up to about 2.5 to 3 cms each in size) will fit into one of these barrels. Larger barrels are needed for larger stones.
However, the best first buy is actually Model 33B, a machine which runs two 3lb barrels, costing NZ$370.75 ($461.45 in March 2022) As at October 2024, Mr Gritsells dual 3lb tumblers from Aussie Sapphire for NZ$379.95. As there can be up to four or five stages of tumbling a batch of stones, taking about five to six weeks in all, [although really smooth stones can be done in two stages, in three weeks], having two barrels makes the process twice as fast. It is important to avoid contamination of grit sizes from one tumble to the next so the barrels need to be cleaned carefully in between batches. (I have five different barrels, each dedicated to one grit/polish size, but there is no problem reusing the same barrel for different grits if attention is paid to cleaning.) With two barrels, one can be used for grits and one for polish. [Note: Rotorua Lapidary from 2021 stocked grits and polish for four stages instead of five, so only four barrels would be needed for strict separations for rough stones. The following two photos are snips from their website http://www.rockandgemstoneshop.co.nz in March 2022. Note: It is also possible to buy extra barrels – a 3lb barrel cost $99.70 in March 2022.]
The next largest barrel is a 4lb one, Lortone Model 45C, currently selling for NZ$359.50 ($452.45.00 in March 2022). It is available only as a one-barrel machine. Stones up to 4 cms big can be polished in this barrel, and it can take about twice as many stones as a 3lb barrel. I also bought one of these a few weeks after starting tumbling because I wanted to polish larger stones than the 3lb barrel could, and it also allows me to tumble more stones at a time. I have no personal experience with any other tumblers.[By March 2022, I also have experience with 6lb and 12lb tumblers – I particularly like working with the 6lb barrels, using a Lortone Model QT66. It takes more and larger stones, is not too heavy to lift and empty etc., though it naturally uses up more grit and polish per load.]
SAY you buy one Model 33B Lortone tumbler = NZ$370.75 ($461.45 in March 2022) (plus postage if buying online)[You can buy an extra barrel or two later should you decide they will be useful.]
Two Lortone 33B Models in the shed, one is mine and one is my wife’s. The motor and frame for a Lortone 45C Model sits to the left. The tumblers sit on plastic trays. Each tumbler is labelled with the Stage it is used for. There is a power point to the left, outside the photo.
2) SITING OF TUMBLER
Secondly, a place to site the tumbler is needed. The following are the main considerations: NOISE – The Lortone tumblers are powered by small electric motors (designed to run 24/7) which are very quiet. When barrels containing stones, water and grit are tumbling, there is also very little noise (less than slowly moving stones in water in a plastic container by moving the container from side to side). I first ran my tumbler in the garage which is attached to my house. It was only just possible to hear a vague noise in the background when in the house. Any other noise will be greater. However, the tumbler operates 24 hours a day, including at night.
After a couple of weeks or so, I moved the tumbler to a shed outside, mainly to have more space. One consideration affecting noise is what the tumbler rests on. A little heat is generated by the electric motor so I decided not to place it on newspaper or any kind of soft material, which would also be noise absorbing. My tumblers sit on a plastic tray which seems to deal with the heat issue fine, but it probably does not minimise the noise of tumbling (but it’s actually very low anyway, and my tumblers are out in a shed). I also initially chose a plastic tray to contain any spilled water but this has never been a problem (the lids on Lortone tumblers are very effective, mine have never leaked and have never blown off).
FLAT AREA FOR TUMBLER – An area at least the size of the tray the tumbler rests on is required.
SOURCE OF ELECTRIC POWER – Needs to be within reach of a power point (though extension cords can be used, of course).
NEAR TO WATER – Water is used a lot in tumbling – it goes in each tumbling barrel and is needed to wash stones coming out of a barrel. Having a water tap within three or four metres of the tumbler is a good idea.
NEAR A FLAT WORK SURFACE – This is needed when sorting stones, filling barrels, emptying barrels, and so on. In my view a minimum of 1 metre by 1 metre at waist height is needed.
NEAR TO STORAGE – Stones, grit, and sieves are among the things that need to be stored or at hand. At least a couple of shelves would do, or a further flat surface such as a table or desk.
We installed a tap and sink in the shed where the tumblers are. Note the flat surface to the left of the sink, where tumblers are loaded and emptied.
Just part of the storage space we have. The top shelf includes barrels not currently in use. The containers on both shelves have stones from different places as well as stones at different stages of tumbling.
3) TUMBLING GRIT – SILICON CARBIDE
Silicon carbide grit of various grades is used in the tumbling barrel to shape and smooth the stones, and needs to be purchased.Usually two or three different grades are used, depending how smooth the stones are at the beginning of the process. Different tumbling practitioners and tumbler manufacturers use or recommend different stages and/or grit sizes (see, for example, Shelby Raymond’s “Rock Tumbling for the Beginner” which uses different grit grades than what I go on to recommend). The following is what I use, based on the recommendations of Colin Simmons (Rotorua Rock and Gemstone Shop) as he sold me my first tumbler, he stocks this grit for sale, and they work well for me. However, remember that variations are not uncommon (different grit sizes).
The coarsest grit I use is 100 grade (Rotorua Lapidary changed this to 80/100 grade in 2021) – this is good if the stones need some rounding or if they have cracks and pits that need removing. I next use 220 grade to increase the smoothness of the stone – many of the stones I collect are off beaches and they are often very rounded and smooth to begin with, so these can often be started with 320 grit, skipping the 100 and 220 grit stages. [Rotorua Lapidary have changed the grit grades they stock – 320 grit has been replaced with 400 – use this instead.]
Colin Simmons in Rotorua sells grit as follows, in March 2022 prices: 80/100 grit, 500 grams = NZ$9.25, 1 kg = NZ$15.55, 2 kgs = NZ$28.60; 220 grit, 500 grams= NZ$9.75, 1 kg = NZ$16.20, 2 kgs = NZ$29.85; 400 grit, 500 grams = NZ$12.35, 1 kg = NZ$21.75, 2 kg = NZ$41.00.See also Mr Grit’s grit prices here. Lortone recommend that 4 tablespoons of grit be used for each 3lb barrel load and 6-8 tablespoons for each 4 lb barrel load (I used to follow these suggestions, but now in October 2024 use less grit, generally one tablespoon per pound for a barrel, plus adding borax – see the last part of my Post “Sunlight Soap, Borax and Tumble Polishing”). I have just measured the number of tablespoons there are in a 2 kg lot of 100 grit (as it was the only unopened grit I had) – there are 90 (and I tried to make each tablespoonful an even one), and thus there is likely to be 45 tablespoons of grit in 1 kg of 100 grit. I suspect there would not be much difference for the 220 and 320 (400) grits (give or take 3 or 4 spoonfuls maybe). This means 1 kg of grit contains enough for about 11 barrels.
In my view, given that someone makes the initial financial investment in a tumble barrel, it would be worth getting 1 kg of each grit to start off with (it is cheaper than the 500 grams size and there may be little to be saved in buying 2 kgs, except maybe postage – but check that as prices can vary over time). [Note: Rotorua Lapidary sells Grit and Polishing Tumbling Kits that will save you a couple of dollars overall.]
SAY you buy 1 kg each of 80/100, 220 and 400 silicon carbide grit = NZ$53.50 (plus postage, if buying online)
TOTAL so far = NZ$514.95 (plus postage)
4) GRIT STORAGE AND TABLESPOON MEASURING
The one and two kg size grits as sold by Colin Simmons come in plastic containers of the kind used for milk in New Zealand. This means the openings are so small that it is impossible to insert a measuring spoon. Pouring the grit out for each batch of stones may not be a good idea because of the risk of spillage. I therefore store my grit in containers that I can easily reach into with a spoon. I tend to buy Sistema plastic storage containers generally because they are good quality and have effective lids. Often they can be bought on sale. I use a 2.4 litre container for both 100 and 220 grit and a 2.2 litre container for 320 (400) grit (this has a stronger set of clips as I wanted greater security for the finer powder) – see the second photo below. However, any container with a lid will do.
In order to avoid cross-contamination of grits, I strongly suggest you buy one measuring spoon per grit size and keep it exclusively in the container with that grit (you might have to buy three sets of cheap plastic measuring spoons if separate tablespoon measures are not sold). Alternatively, one metal tablespoon could be used as long as it is cleaned after each use.
SAY you buy three containers for NZ$38 and three tablespoon measuring spoons for NZ$12 = NZ$50
TOTAL so far = NZ$564.95 (plus postage)
The middle shelf here contains the grit containers. The top shelf has the polish powders and plastic beads.
The three grit containers. Note the white measuring spoon in each.
You need a means for disposing or storing the slurry that results from tumbling. This slurry consists of water and broken down grit and tiny rock fragments (it would be a fine dust if it was not wet). This slurry should never be put down a household drain as it will settle into traps, turn into concrete and ruin the plumbing. I pour it into a bucket. I then pour the water off the top of the bucket as the sediment settles, a number of days later. A fine sediment builds up a number of layers after a number of slurries are poured into the bucket. The sediment can be disposed of in a hole dug outside, or in the household rubbish collection etc. I have a number of buckets next to my water tap for this purpose.
Buckets used for slurry.
When we installed the sink in my shed, we attached it directly to a hose which runs a few metres out onto the ground – this means we are able to wash minor amounts of slurry down the sink drain without it blocking anything. (It’s also a good idea to avoid getting any slurry or grit, which is silicon carbide, onto clothes or towels etc. which are then washed in a washing machine as the slurry and grit can damage the machine and drains.)
SAY you buy one 10 or 20 litre plastic bucket for NZ$10
NOTE: March 2021. My supplier now stocks 400 grit instead of 320. So now Stage Four is a 400 grit tumble with the grit being a little finer. However, the change makes no difference to what happens during Stage Four, it’s just that 400 grit is used instead of 320. But it does allow a one-stage polish process to be undertaken afterwards. Details can be found in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage.
There are seven stages in the tumble polishing of stones. The first stage is acquiring the rough stones. Stage Two involves tumbling rough stones in a solution of water and 100 grade silicon carbide abrasive grit. Stage Three entails tumbling the now smooth stones in 220 grade grit. The 40 Riverton stones being tumbled for this series of Posts were next placed in 320 grade grit, Stage Four, on 10 March after I had returned from my South Island stone collecting trip. This Post is the sixth in this series, the first Post being here.
Note that in this series I have counted the collection of stones as Stage One. Nearly all other accounts of tumble polishing call the first actual tumble Stage One whereas I have called it Stage Two – and this affects the numbering of all subsequent Stages.
Furthermore, while I initially put nearly all the stones I collected through Stages Two, Three and Four, I no longer do this as a matter of course. More often these days, I consider starting a stone at Stage Four, some of them I start at Stage Three, and I rarely start a stone at Stage Two. This is because I mainly collect smooth beach stones that do not need shaping and/or smoothing as much as stones found in rivers or on dry land.
So, for Stage Four, I place the 40 Riverton stones in the 4lb tumbling barrel. Water, plastic beads, and 320 grit are then added. I use about 16 tablespoons of beads to bring the load level up to about two-thirds, as the stones have gotten smaller with each tumble. I don’t usually put just the same load of stones through each stage – I usually do two or more loads at the lower grit grade and then sort each load in relation to which Stage they should go to next. In this way I am able to collect enough stones for a good-sized load for each stage.
I use a number of compartmented plastic trays, 45 cms long, 30 cms wide and 8 cms deep, for sorting and storing stones in order to collect enough for a tumble load.
Back to the Riverton stones being tumbled for this series on the Stages of tumbling:
As with Stages Two and Three, I add water and seven tablespoons of grit (320 grade) to the barrel for Stage Four. I then tumble these stones for nearly 10 days. The recommended time for Stages Two, Three and Four is seven days each but this is a minimum and I often leave the tumbler going for another three or four days per stage.
So, after nearly 11 days tumbling, I empty the tumbler into a stainless steel strainer (sieve) labelled for 320 – it is used only for stones straight after being tumbled in 320 grit (to prevent contamination with other grades of grit).
Sieves for the different grit and polish grades
The strainer is placed over a bucket and I run water over the beads and stones to wash the slurry away. I then clean the empty barrel, using a toothbrush labelled for “320” use, also using a paper towel (as previously described in detail for Stage Two).
After thorough washing, I put the stones back in the barrel. I add water along with a few flakes of sunlight soap and place the barrel back on the tumbler. In this case, for these 40 stones, I tumble them in soap for just over three days. Sometimes I run a soap tumble for only a day, but as I am going to re-use the 4lb barrel for the next stage, pre-polishing, I want it to be as clean as possible to avoid contamination with previous grit.
So on Friday morning, 23 March, I empty the soap-tumbled stones out of the barrel and wash them and the barrel.
Taking the lid off the 320 grit tumble.
Washing the stones after the 320 soap tumble.
The 40 Riverston stones fresh out of the soap tumble folloing the 320 grit tumble.
The amount of plastic beads used with the 320 tumble.
The water from the post-320 soap tumble – significant additional slurry is removed from the stones and barrel.
Once the stones are dry I put them on the scales and discover they weigh 1261 grams.
At the start, before any tumbling, the stones weighed 1605 grams, losing 8.4% of that weight during the 100 tumble (ending up weighing 1470 grams after the 100 stage). During the 220 grit tumble, 9.3% of this 1470 grams was lost (the stones ending up weighing 1353 grams). Stage Four, the 320 grit tumble, resulted in a reduction of a further 92 grams, which is 6.8% of 1353 grams. In total, through Stages Two, Three and Four, the stones have lost 344 grams of their original weight of 1605 grams, which is 21.4%, just over one-fifth.
The amount of material lost during tumbling is dependent on a number of factors – the length of tumbling, the softness of the stones, any chips lost from the stones, and so on.
The next Post is about the state of the stones after the 320 grit tumble.
Stage Three in tumble polishing involves tumbling stones in 220 grade silicon carbide grit. (The first Post in this series, using 40 Riverton stones, can be found here.) Usually stones tumbled in 220 grit have already been tumbled in 100 grade grit (Stage Two), mainly to “shape” them and start the surface smoothing process. Sometimes a stone found on a beach or river bank may already be well rounded and smooth and it can skip Stage Two. The following outlines what is involved in Stage Three and some of the preparation for Stage Four, including sorting and inspection.
I place the 40 Riverton stones in the 4lb tumbling barrel. Plastic beads, water and 220 grit are then added. I use about 14 tablespoons of beads to bring the load level up to about two-thirds. Each stage of tumbling reduces the size of the stones so progressively more beads are needed unless additional stones (which are of a similar smoothness etc.) are added. As with Stage Two, I add seven tablespoons of grit.
The stones, the plastic beads and the 220 silicon carbide grit
All 40 stones do not fill up 2/3 of the barrel which is one of the main reasons why plastic beads are then added
220 grade grit is finer than the 100 grade grit used in Stage Two
Everything has been added to the barrel and the lid is then placed on and the barrel set to tumble for at least 7 days
I tumbled these stones for nine days and two hours (seven days is the minimum recommended time). Sometimes I may tumble a Stage Three barrel for longer, up to 11 or 12 days, depending on the state of the stones and whether I am preoccupied with other things.
I empty the slurry from the barrel, wash the stones, clean the barrel and then tumble the stones in about a teaspoonful of grated Sunlight soap for 18 hours (in the same manner as described in my earlier post on Stage Two). This soap wash is very important not only to remove the last of the slurry from the stones but to clean the barrel before the next Stage. I have only one 4lb barrel so I am using it for all Stages. To minimise contamination of one grit by another, thorough washing is required.
Opening the barrel after 9 days of tumbling with 220 grit
Pouring the slurry out. The plastic beads are apparent
The stones appear, covered with the slurry
After the slurry has been washed off
After washing for 18 hours in soap, to clean the stones and the barrel, the mix is again poured out and rinsed in water
The resulting product
The weighing
When I weigh the washed stones, they come to 1333 grams, having started the Stage at 1470 grams. This means they have lost 137 grams or 9.3% of their mass. This is more than expected, given that they lost less, 8.4%, during Stage Two. Generally speaking, I find that much more is lost during Stage Two (100 grit tumble) compared with Stage Three (220 grit tumble). This batch of stones is unusual in this respect, and I am unsure why. Right at the beginning, before Stage Two, they weighed 1605 grams so the two tumbling stages have entailed the loss of 272 grams which is 16.9% of their weight.
In a previous Post, I described the inspection of each stone after the 100 grit tumble. I do the same inspection after the 220 grit tumble, to check that each stone is ready to go on to Stage Four to be tumbled with 320 grit. In general, the smaller marks and pits on the stones should be worn away but this does not always happen.
For example, Stone 11 had a very minor superficial crack before Stage Three. Afterwards, it has been significantly smoothed out:
Stone 11 before 220 grit tumble
Stone 11 after 220 grit tumble
You will note some differences in the before and after colours of the stones in this Post, due to the fact that lighting conditions were different when the photos were taken.
Stone 19 has also had a small crack made less pronounced:
Stone 19 before 220 grit tumble
Stone 19 after 220 grit tumble
These stones would in fact benefit from another tumble in 220 grit for a week to further reduce these “imperfections”.
The other stones with larger cracks and pits emerged from the 220 tumble with them reduced but but still apparent. For example, Stone 1 has a number of small pits that arise because it is a stone of volcanic origin with small gaseous pockets. Wearing away the stone will often simply reveal and expose more such pockets:
Stone 1 before 220 grit tumble
Stone 1 after 220 grit tumble
Such a stone as Stone 1 will always have these problems in gaining a smooth surface but it can still polish with some success.
Stone 15 has a small gouge in the side that has smoothed somewhat but by no means in a significant way:
Stone 15 before 220 grit tumble
Stone 15 after 220 grit tumble
A stone like this needs to be re-tumbled in 100 grit.
The surface crack in Stone 20 is still noticeable and requires at least another tumble in 220 grit:
Stone 20 before 220 grit tumble
Stone 20 after 220 grit tumble
The medium-sized pit in Stone 9 is still apparent, as is the deeper pit in Stone 10:
Stone 9 before 220 grit tumble
Stone 9 after 220 grit tumble
Stone 10 before 220 grit tumble
Stone 10 after 220 grit tumble
I would normally seriously consider discarding Stones 9 and 10 and not continuing with them due to these problems. Putting them through the whole polishing process would likely result in the white polish accumulating in the pits and blemishing the finished product. The rest of the two stones would polish quite well but my preference is to try to produce a uniformly polished stone. The only exception would be a stone of significant interest, too valuable for its beauty to discard for a partial blemish. However, for the sake of the demonstration in this series of Posts, I will put all 40 stones through the next stage of tumbling.
I will end this Post with some photos showing the relative sizes of the stones being tumbled. The larger the stone, the more you can tumble it, the more often you can repeat a stage. The smaller the stone, the more likely it will wear away to very small or nothing in the tumbling process. At this stage in the polishing, Stage Three, Stone 1 is approx 7.75 cm long and 4.5 cm wide, Stone 20 is 4.25 cm long and 3.75 cm wide, and Stone 40 is 1.75 cm by 1.5 cm.
Comparative sizes of Stones 1, 10, 20, 30 & 40
Comparative sizes of Stones 1, 7, 16, 26, 35 & 39
Comparative sizes of Stones 1, 25 & 40
I am about to hit the road for four weeks, travelling to the South Island, including to Riverton again where more beach stones will be collected. So there will likely be no more Posts for at least this time.
