A Blog About Stone Gathering, Tumbling and Polishing, and Rocks and Landscapes, from New Zealand – With Musical Interludes (john.tumblestone@gmail.com)
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
Next stop was Riverton at the very bottom of the South Island, where we were based for the next three weeks – many thanks to Helen and Ray for the generous use of their holiday home. We collected many beach stones from the Riverton area and from nearby Gemstone Beach at Orepuki. The weather was cool and windy at times but not bad enough to discourage stone collecting. We met a handful of fellow stone collectors at Gemstone Beach and exchanged greetings and stories. We also spotted dolphins swimming off the beaches at Riverton.
Riverton’s Back Beach, a great source of stones to polish
Fossicking for stones, Back Beach, Riverton
Crashing waves, Back Beach, Riverton
Hector’s dolphins, Riverton
Hector’s dolphins, Riverton
Along the coast from the Back Beach, Colac Bay hill in the background
A stormy day, Riverton coast
Gemstone Beach, near Orepuki
There were many stones exposed on Gemstone Beach
While based at Riverton, we took a day trip eastwards to Waipapa Point, Slope Point and Curio Bay, the latter being well known for its petrified forest that is uncovered at each low tide.
Waipapa Point lighthouse
Sea lion emerging from the surf at Waipapa Point
Waipapa Point
Slope Point is the southernmost part of the South Island
Rough seas at Slope Point
The stairs down to Curio Bay
Petrified fallen three at Curio Point becomes apparent as the tide recedes
Petrified tree stumps at Curio Bay
Petrified wood in the rocks at Curio Bay
Petrified tree stump, Curio Bay
One day we walked the Long Hilly Track through an old gold mining area near Orepuki. This included part of the 40 kilometre long Port’s water race, built in the 1870s and 1880s with the help of Chinese miners. We visited the Riverton Museum and found an excellent display on the Chinese goldminers. On a visit to the Southland Museum in Invercargill, we saw a natural history room that included a lot of local geological displays and information.
Round Hilly Track information panel.
Most of the track is through bush like this. It was a cold wet day.
About Port’s water race – 40 kms long
Port’s water race runs alongside the track for hundreds of metres
Ray starting at the bottom of part of Port’s water race
At times Port’s water race runs through short tunnels
Dams were constructed to feed water races for the gold mining.
An area behind one of the dams.
Information panel on the Chinese gold miners
A substantial Chinese settlement is now only bush
The southern-most Chinese settlement in the world
On the trip north, on the way home, we stopped off to see the Moeraki Boulders in North Otago. Some sea mist came down even though it was the middle of the day. The boulders are large spherical rocks, concretions that have been exposed through shoreline erosion from coastal cliffs. They consist of mud, fine silt and clay, cemented by calcite. The degree of cementation varies from being relatively weak in the interior of a boulder to quite hard at its outside rim. The boulders are cracked and eventually fall apart after having been exposed for some time.
Tourists in the midday sea mist at the Moeraki Boulders
The Moeraki Boulders are a popular tourist attraction
Moeraki boulders on a misty midday
Moeraki boulders
The boulders originate in thecliffs behind the beach
The boulders eventually collapse
A day was spent at Birdlings Flat, near Christchurch, where we collected quite a few stones for polishing. We walked to the point where the stony beach meets the volcanic mass of Banks Peninsula, briefly disturbing a resting seal. The tide was low enough for us to look at the stones in the small bay past the seal.
Birdlings Flat stones, among the best to polish
The seal that I stumbled upon
Going as far as possible at the Banks Peninsula end of Birdlings Flat
We also took the opportunity to visit Akaroa on Banks Peninsula where we saw thick clouds rolling slowly down over the hills.
Clouding rolling down the hills at Akaroa
Akaroa clouds
The road further up the east coast of the South Island, through Kaikoura, was open – it had to be rebuilt after the November 2016 magnitude 7.8 earthquake as well as additional landslides caused by recent storms. So we were able to view the earthquake aftermath, including the land that been raised out of the sea. Some parts of the coast were uplifted by six metres. One of the places we visited on the Kaikoura peninsula was Point Kean, well-known for its seal colony. A large area of many hectares/acres now lies dry where it once was under the sea.
Large uplifted area, formerly under the sea, at Point Kean, Kaikoura
Point Kean, Kaikoura, land uplifted out of the sea by 2016 earthquake
Pont Kean, Kaikoura, looking back to the parking area
Seals are very relaxed about the people walking around at Point Kean, Kaikoura
Lounging seal, Point Kean, Kaikoura
Rain water pool on rocks previously under the sea
The sea looks a long way away
Off Point Kean, Kaikoura
Some interesting folded rocks have been exposed by the earthquake
Newly exposed folded rocks, Point Kean, Kaikoura
Then it was home across Cook Strait, a choppy but not uncomfortable crossing.
Leaving the South Island on a Cook Strait ferry
Passing another ferry in the middle of Cook Strait
I have recently returned from a few weeks in the South Island of New Zealand, travelling by car, collecting stones from places like Charleston, Riverton, Orepuki and Birdlings Flat and visiting interesting landscapes like the limestone caves and arches of the Oparara Basin (north of Karamea), Arthurs Pass, Lakes Pukaki and Tekapo, Curio Bay, Waipapa Point, the Moeraki boulders, and the post-earthquake Kaikoura coast.
One of the first places we stayed at was Karamea in the north Buller region of the West Coast. From there we drove the narrow gravel road north to the Oparara Basin and walked to the Oparara Arch, Moria Gate and other limestone caves and landforms.
Oparara Arch, towering high up, a limestone feature
The cave beneath Oparara Arch
In the Oparara River, just below the Oparara Arch
Moria Gate, another limestone arch/cave
Looking out of the cave onto the river at Moria Gate
Looking upstream at Moria Gate
Moria Gate limestone, in the cave
Inside the “Crazy Paving Cave”, Oparara Basin – the patterns are made by dried mud
A rare protected native spelungula spider on the wall of the “Box Canyon Cave”, Oparara Basin
We saw a lot of wekas in the Buller/West Coast area – a cheeky native flightless bird. This one was in the Oparara Basin carpark.
I collected a small number of limestone stones from the Oparara River – they appear to have fossilised shells in them.
Going south along the West Coast, beyond Westport is the town of Charleston and its small twin bays, Constant Bay and Joyce Bay. Constant Bay was named after the ketch “Constant” whose Captain, Charles Bonner, in the mid 1860s managed to squeeze the boat into into the tiny bay, bringing supplies for the town that had sprung up due to the discovery of gold. The rocks that line the shore of these bays have large veins of quartz with masses of mica in them. At the northern end of Joyce Bay we came across of pocket of stones and rocks from a vein that must have been almost pure mica. We chose one small boulder-sized rock to bring home.
Constant Bay
Veins of mica-rich quartz in rocks at Constant Bay
Another detail of Joyce Bay mica rock
Masses of mica in rock at Joyce Bay
Mica in quartz vein, Constant Bay
Rock brought home from Joyce Bay. It must be at least 95% mica. Large mica piece at bottom centre, other pieces of mica throughout the rock
Detail of Joyce Bay rock made up primarily of mica
There is so much mica in the rocks around Constant and Joyce Bays that the sea sparkles with it.
One hundred kilometres south of Charleston is Kumara, where we undertook a short walk to see Londonderry Rock. This enormous 4000 tonne glacial erratic was dislodged by miners while sluicing for gold in the early 1880s. As noted on the information panel at the start of the walk, local legend has it that when it was dislodged from its position it caused earthquake-like shudders that stopped the clock in the post office!
Information Panel at start of the short walk, near Kumara
4,000 tonnes Londonderry Rock; Petra standing to the right side
Londonderry Rock, towering and massive
Along the track are many large boulders left over from the gold sluicing
Hidden in the bush, large piles of boulder tailings
The clock stopped!
Driving across Arthur’s Pass, we passed Castle Hill, Omarama and Lakes Pukaki and Tekapo.
Castle Hill limestone outcrops
The clay cliffs near Omarama
Omarama’s merino sheep statue
Aoraki/Mt Cook, New Zealand’s highest point
Lake Tekapo
Lake Teakapo, with Aoraki/Mt Cook in the distant clouds
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.
(This is the fourth Post in this series, the first one being here.)
Stage Two in tumble polishing involves tumbling rough stones in 100 grade silicon carbide grit. Stage Three involves tumbling in 220 grade grit. In between these stages, and in between later stages, I inspect each dry stone in a good light to check that it is suitable to go on to the next stage. Sometimes it may need to repeat a stage, or it may become apparent that there is a reason to discard a stone entirely.
The following presents the 40 Riverton stones after the 100 grit stage then describes their inspection and sorting. This initial stage of tumbling has resulted in smoother stones, and their colour is now more apparent.
Stones 1 to 5, dry then wet:
Stones 6 to 10:
Stones 11 to 15:
Stones 16 to 20:
Stones 21 to 25:
Stones 26 to 30:
Stones 31-35:
Stones 36-40:
INSPECTING AND SORTING
I inspected each stone when it was dry. I sat under a bright light and simply held the stone and turned it around. I found that 22 of the 40 stones are nice and smooth with no chips, nicks or pits. Some of these could skip the next stage and go straight to being tumbled in 320 grit but for the sake of this series of Posts I will keep them with the others for tumbling in 220 grit.
Five stones (5,11,12,19 & 28) have very minor cracks, pits or slight gouges. Here are two examples: Stone 11 has a very minor superficial crack.
Stone 19 has a couple of very small superficial cracks as well, one of which is indicated below.
Such very minor “imperfections” are usually easily removed in the 220 grit tumble.
Eight stones (1,2,15,20,23,26,34 & 39) have small or medium-sized pits or cracks. These also usually disappear after tumbling in 220 grit. Three examples: Stone 1 has a number of small pits.
Stone 15 has a small gouge in the side.
Stone 20 has a small surface crack.
Three stones have issues that I would normally hesitate over for some time, considering whether to tumble them again in 100 grit. Stone 4 has a small indentation in its side.
Stone 25 has a number of noticeable cracks and pits in it. It is one of the smaller stones.
Another small stone, Stone 31, has some chips on it. It is easier to get rid of such chips if the stone is larger because it can stand up to losing another 5% or more by repeating the 100 grit tumble. But because it is so small, it can be worth trying the 220 grit tumble first to see if it improves without losing too much of its mass.
Finally, there are two stones that I would normally put back to another 100 grit tumble. Stone 9 has a medium-sized pit in its side.
Stone 10 has an even deeper hole in it from where a small embedded piece of stone has loosened and come out.
One year later, the “milestones” are still functioning as intended. Charlotte posted a comment and photo on Facebook:
“Someone came to replace my computer at work and noticed my milestones. They sit on my desk and are a reminder of how anything can be achieved one small step at a time. Still some of my favourite things and a wonderful reminder of each small step and the people who helped along the way.”
In Maps as a Resource: New Zealand’s “Maps Past”, Part One and Part Two, I demonstrate ways in which the “Maps Past” website provides maps of interest to researchers. The following is a step-by-step introduction to using the website for those who might find it useful.
Step One: Go to http://www.mapspast.org.nz. The following (or something similar) is likely to open as the home page:
The next two steps are aimed at getting rid of unnecessary material from the screen before zeroing in on a location of interest.
Step Two: Get rid of the “Select basemap” pop-up menus by clicking on the “x” on it (circled in black on the image below):
Step Three: Remove the text material from the lefthand side of the page by clicking on “Mapvv” (partly circled in black in the image below) which is on the righthand margin at the top:
This then should leave you with a map of New Zealand and seven icons at the left top of the page:
The seven icons are:
From left to right:
White plus and minus signs on blue background = Zoom in/Zoom out.
Three layers icon = “Select basemap” = Brings up list of 14 options, most of them decades.
Cog icon = “Map options, Coordinate format” = Brings up list of 11 options.
White i in blue circle = “Show mapsheet details for current series when you click on the map”.
Clipboard list with white i in blue circle on bottom right corner = “List all available mapsheets at point you click on the map”.
Magnifying glass with three arrows = “Zoom to extent of current mapsheet/series”.
Two chain links = “Show URL of currently displayed map”.
Below I will discuss the use of four of these icons – the first, second, fourth and fifth. I have found that I can achieve what I want through using these four.
Step Four: Use the “Zoom in” icon (white plus sign on blue background at top left of screen) to zoom in to the location you want to examine. You are likely to also need to move the map to bring your intended location to the centre of the screen – move the cursor to somewhere on the screen, click and hold, then move the cursor – this will move the map. I have chosen to zoom in on Riverton at the bottom of the South Island (see below). At the bottom right hand of the screen are some figures, the scale of the map on screen, the map sheet or series, and co-ordinates of the cursor. In this case, for example, there is “Scale = 1 : 27K” (27K = 27000) and “NZTM2000” map series. This information may or may not ever be of use to you.
Step Five: Once you have zoomed in to the location you want, at the scale or level of detail you want, you can then click on the “Select basemap” icon (three layers icon) at the top left to choose which map you want to see.
I decided to try to find the earliest map. I clicked on the fourth last map “NZMS13 1899”. The list then disappeared and the screen went blank. This means such a map does not exist. I clicked again on the “Select basemap” icon to bring the list of maps up again, and clicked on “NZMS13 1909”. Same blank result. When I next clicked on “NZMS13 1919”, the following map came up:
The 1929 map was the same. The 1949 map was not at a good level of detail:
But the 1959 map was a good one:
And we could go on, choosing more recent maps or the air photo…
Step Six: Finding out what maps are available for the location. To do this, you click on the icon of a clipboard list with white i in blue circle on bottom right corner – this is to “List all available mapsheets at point you click on the map”. This icon turns green when you click on it. You then click on a point on the map and a popup list appears which you can scroll down. This lists all maps that have been published or are available for this location.
The earliest map listed for Riverton is Series: NZMS13 Sheet: SD58, Printed: 1910. This will be why no map came up earlier for 1909 but one came up for 1919 when I was using the “Select basemap” icon.
Step Seven: Finding out which map you are viewing. When a map is on the screen, you can use the icon of the white i in blue circle = “Show mapsheet details for current series when you click on the map”.
This icon also turns green when you click on it. You then click on a point on the map and a popup list appears which identifies the map that is being shown. In the case above, the 1910 map is identified even though the map came onto the screen originally when I was using the “Select basemap” icon and had chosen “NZMS13 1919” from its menu list. In other words, the decade menu list that appears when you click the “Select basemap” icon does not mean that the map that comes up was published the year shown (1919 in this case) but it may have been earlier (1910 in this case).
