Rock Tumbling Practicalities – Page 2

Six Past TumbleStone Posts of Interest to Beginning Tumble Polishers

1) What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?

This two part series sets out what a beginning tumble polisher needs and how much it will cost. The costs and details reflect that I live in New Zealand, and the prices were accurate at the time of writing, April 2018. The account aims to be fairly thorough and realistic. Part One covers: The Tumbler; The Siting of the Tumbler; Silicon Carbide Grit; Grit Storage and Tablespoon Measuring; and Disposal of Slurry. Part Two covers: Tin Oxide Polish Powder; Polish Powder Storage and Mixing; Plastic Beads and Bead Storage; Soap for Cleaning and Burnishing; Sieves and Buckets; and Miscellaneous Useful Items.

NOTE: Due to changes in the supply of grit and polish (late 2020), these Posts have been revised (the changed text in the original Posts are in light green). Background details can be found in UP-DATE OF “What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?” Changing Prices, New Grits and Polish.

2) The Seven Stages in Tumble Polishing Stones

This at-present-incomplete Series goes through, step-by-step, the seven stages of polishing stones using a tumbler and 4lb barrel. A set of 40 beach stones collected from Riverton are used to illustrate each stage. Lots of photos show all the steps involved, often following individual stones (the stones are numbered 1 to 40). Stage One is Stone Collection (not usually included in accounts of tumble polishing). Stage Two is tumbling the stones for about a week in 100 mesh silicon carbide grit, then tumbling them in a soap wash for a few hours. Stage Three involves one week tumbling using 220 mesh silicon carbide grit, followed by a soap wash. Stage Four is the same procedure with 320 silicon carbide grit. Stage Five involves tumbling the stones in a tin oxide “Pre-Polish” powder (five microns in size) for three to five days, followed again by a few hours soap tumble. Stage Six is the “Pro-Polish” tumble, using tin oxide powder of one micron size, for at least one week. Stage Seven is a “burnishing” tumble for a week in borax. Inspecting and sorting of the stones also take place after each Stage.

NOTE: Due to changes in the supply of grit and polish (late 2020), six stages are now used – details can be found in UP-DATE OF “The Seven Stages in Tumble Polishing Stones” – One Less Stage.

Posts in the original Series to date are:

Stage One, Stone Collection, Riverton, 2-6 November 2017 – Topics include walking the beach, selecting stones, clothing, and equipment.

The Selected 40 Stones – Photos of the rough stones, dry and wet, and brief descriptions.

Stage Two, 100 Grit Tumble, 15-25 November 2017 – Step-by-step account of preparing the barrel and then emptying it after the tumble, disposal of slurry, cleaning of equipment, undertaking a soap wash afterwards, and finally determining weight loss of stones.

The Stones After 100 Grit and Their “Inspection” and “Sorting” Before Stage Three – Photos of the stones are presented after they have been through the 100 grit tumble, then an account is provided of the inspection of the stones, identifying the types of chips and holes and other “imperfections”.

Stage Three, 220 Grit Tumble, 4-13 December 2017 – This Post not only goes through the practicalities involved with the 220 grit tumble but also the inspection of the stones afterwards.

Stage Four, 320 Grit Tumble, 10-20 March 2018 – A repeat of the steps involved in Stages Two and Three but this time with 320 silicon carbide grit.

The Stones After 320 Grit and Their “Inspection” and “Sorting” Before Stage Five – Some minor issues with a number of stones are presented, illustrated with photos.

Stage Five, Pre-Polish Tumble, 28 August to 3 September 2018 – Includes an account of preparing the tumble and the soap wash afterwards.

The Stones After Pre-Polish and Their “Inspection” and “Sorting” Before Stage Six – This Post includes photos showing all 40 stones as they looked upon initial collection from the beach at Riverton and then upon completion of Stage Five, Pre-Polish, with the stones sitting on graph paper for size comparisons.

Stage Six, Pro-Polish Tumble, 1 October to 15 October 2018 – An account of tumbling in 1-micron Pro-Polish tin oxide powder.

Stage Seven, Borax Burnishing Tumble, 15 October to 25 October 2018 – Instead of undergoing a short soap wash after the Pro-Polish tumble, the stones are treated to at least one week’s tumbling in borax to help bring out the shine a little more. A summary of the tumbling stages and times is provided at the end of this Post.

The End Result, Stones One to Five – This Post examines how the first five of the 40 Riverton stones have emerged from the polishing process, comparing them with how they looked as rough stones fresh from the beach. Each stone is discussed and close-up photos are provided of their textures, colours and patterns.

The remaining Posts to date are How Stones Six to Ten Have Polished and The Fate of Stones 11 to 15. To Be Continued…

3) The Best Rock Tumbling Book Around – “Modern Rock Tumbling” by Steve Hart (2008)

I read the book referred to in this Post after only a couple of weeks of my own tumbling venture and found it directly relevant and immediately useful. It remains the best I have come across. It is available both as a “real” (paper) book and an e-book.

4) Sources of Detailed Instructions for Tumble Polishing Stones

This Post is a list of seven sources I have found useful for the beginning (and also for the not-so-novice) rock tumbler. They share a number of things in common but often have their own unique ideas or pieces of advice.

5) How Stones Tumble in a Rotary Tumbler

A video is referred to in this Post showing the tumbling action when a barrel is too full or not full enough. A great help in understanding why a barrel should not have too many stones in it!

6) My New Sorting Container for Stones at Different Stages of Tumble Polishing

A good way to store stones which are destined for different stages of tumbling is presented in this Post, so you can group them until you have enough for a barrel load. This also enables you to inspect stones after a tumble and feel free to set aside those that need to repeat a stage.

My New Sorting Container for Stones at Different Stages of Tumble Polishing

Often I need to store stones at different stages in the tumble polishing process. This is because of the “sorting” I do between stages. After each stage, I look at each stone to decide whether it is able to proceed to the next stage, needs to repeat the same stage, or maybe even go back a stage. Often, then, I may not have enough for a barrel load for the next stage. A plastic container, like a two-litre ice cream container, is useful to store together stones destined for a particular stage. But if I am trying to keep track of stones from different beaches, or different types of stones, it is more efficient to have a multi-compartment container.

On the beach, I use plastic backs like these when collecting stones. I then consolidate them like this to get them home in my suitcase. From here (on the floor at home), they move to the shed where my tumblers are.

Close-up of some of the stones brought home in May 2019.

In the shed, I often store rough stones (and others) in two litre ice cream containers, writing identification on the side of the container.

For a while now, I have been using a four-compartment “Sistema”-brand plastic tray that I bought from the Warehouse in New Zealand. However, this tray is no longer produced, it also has its limitations, and I needed a replacement. Its limitations involve the number of its compartments and its overall size. Regarding the number of compartments: I dedicated the four compartments to stones to go to 100 grit tumble, to 220 grit tumble, to 320 grit tumble, and to pre-polish tumble. This meant I had no compartment for stones to go to pro-polish tumble, needing to keep them separately. In hindsight, it would have been better to replace the 100 grit compartment with a pro-polish one, keeping the rough stones in a separate container.

Sistema storage/sorting tray. My loupe/magnifying glass is in the bottom middle compartment

Sistema storage/sorting tray

Regarding the overall size of the tray: it is just a bit too big to place on the work bench I use when loading tumblers (it is 47 cms long, 29 cms wide and 8 cms deep). And when over two-thirds full, the tray can be quite heavy to move around, and the weight also puts strain on the centre-placed carry handle. Recently, I have been working with more stones than previously, and I need another way of storing them.

I looked around at different shops for an alternative container, and found a very useful one at the Warehouse – the “Taurus” set. This consists of a large tray, larger than the previous Sistema one, that does not have compartments (it is 57 cms long, 39 cms wide and 10 cms deep). I also bought a number of separate containers (“trays”) that can be placed within it. The medium-sized tray is 22 cms long, 15 cms wide and 5.5 cms deep. The small-sized tray is half that size – 15 cms long, 11 cms wide and 5.5 cms deep. The cost of these is very reasonable.

Larger container with no compartments.

Comparison of container sizes, old (below) with new (top)

The new container

The medium internal container/tray.

The beginning of one arrangement – three medium trays along the top

The small internal container/tray.

Two small trays fit in one medium tray.

This provides much greater flexibility. Trays can be labelled as I wish – I can have a number for one particular stage, if I choose. I use a “permanent” marker to write the next tumbling stage on the trays. Methylated spirits can be used to remove this writing, when desired. And I can carry just the relevant tray of stones over to the work bench when filling a tumbler barrel, no need to bring the whole large container. Compared with the previous container, it is easier to move this one, even when it is heavy with stones, because there is a sturdy handle on each end. The handles allow me to move the container on and off a storage shelf with more confidence. The container also fits nicely on the arms of a “director chair” which can be moved about the shed next to wherever the stones are being worked on.

Three medium trays and three small trays fit neatly into the large container

One configuration of trays

Each individual tray is easy to take out if I want to work with the stones somewhere else

A container fits nicely on the arms of a “director chair”

The markers I use to write on the trays

The Seven Stages in Tumble Polishing Stones: The Fate of Stones 11 to 15

This is the 13th Post in this series on the tumble-polishing of 40 Riverton stones, which starts with stone collection and goes right through six different tumbling stages. The first Post can be found here.

The previous Post examined how Stones six to ten came through the tumble-polishing process. This Post looks at Stones 11 to 15, discussing how many of them experienced some damage but still polished well enough to come out looking very interesting:

11-15 rough — Stones 11 to 15, rough, as collected

11-15 polished — Stones 11 to 15, after polishing

STONE 11

Stone 11 is probably a sandstone. In general, it has polished very well, and details of the sand grains that make it up have become clearer to see. This, along with the thin red band and darker base, makes it an interesting stone.

Stone 11, polished.

Other side of Stone 11, polished.

Top of Stone 11, polished.

Detail of Stone 11, polished

There are some problems with it, however. When I inspected it after tumbling in 100 grit, I noted that it had a very minor superficial crack on one side, near its base. After the 220 grit tumble, this had been reduced. This crack remains, though in a reduced state, and can barely be felt when I rub my thumb over it. There are three other similar superficial cracks on the base of the stone, in the dark area. I had seen them at the inspection of the stone after Stage Two but did not think them to be significant. They were not noticeable after the 320 grit tumble. However, they have reappeared, including a long one along the base, and a smaller one on the side can be felt more distinctly than the others.

Stone 11 after 100 grit tumble – crack on side at base

Same crack after polishing and burnishing – reduced.

Long crack along base of polished Stone 11

Most noticeable crack on polished Stone 11

There are no “imperfections” in the rest of the stone, which is lighter in colour – maybe the darker section is just a little more brittle. The fact that these superficial cracks are still there after the various tumbling stages suggest that further tumbling in, say, 320 grit may not remove them. Maybe it would take a 220 tumble to achieve this, at the expense of making the stone a little smaller.

STONE 12

Throughout the tumbling process, Stone 12 exhibited some fragility. Small chips were lost from it now and again, caused by bumping into other stones in the barrel. Even in the pre-polish barrel, it lost two or three small pieces. This is a pity because it is a gorgeous stone with a very interesting make-up. It has an obvious crystalline character which means it is probably quartz, stained with shades of cream. And apart from where it was chipped, the stone has polished very well.

Stone 12, polished

Other side of Stone 12, polished

Detail of Stone 12, polished

Chip out of the end of Stone 12, polished

Small pieces missing from the side of Stone 12, polished

More damage on Stone 12, polished

I put Stone 12 through to the final polishing stages though normally I would have discarded it or returned it to a 320 tumble once or twice. As a result, there are distinct imperfections with the final polished stone.

STONE 13

Stone 13 has polished very well. There are no scratches or holes obvious to the eye to when I rub my thumb over it. Polishing has brought out a complex pattern of colour, grayish purple patches drifting on a green background, with white quartz veins slashed across it.

Stone 13, polished

Other side of Stone 13, polished

Detail of Stone 13, polished

When a dry stone, straight off the beach, Stone 13 had a weathered dull look, though when wet it revealed some of its promise (as can be seen in the photos of Stone 13 in The Seven Stages in Tumble Polishing Stones: The Selected 40 Stones). My guess is that Stone 13 is some kind of metamorphic stone but I struggle to identify it further than that.

STONE 14

Stone 14 is pink granite, though at the darker shade end. This identification is made partly on the basis of information provided by Te Hikoi The Riverton Museum. It has developed an outstanding chidren’s rockhounding kit which includes pink granite as one of the kinds of stones that can easily be found along the south coast of Southland. The museum has a display supporting the kit, and has a set of drawers with rock samples in them.

Riverton Museum, display supporting children’s rockhounding

Riverton Museum, in a drawer, part of rock display

Riverton Museum, poster on different kinds of rocks

The granite rock displayed in the Riverton Museum poster

One of the problems with granite, for the tumble polisher, is that it consists of grains of feldspar, quartz and mica. Depending on how tightly these grains are packed together, the tumbling process may dislodge some as the granite stone bumps against other stones. Furthermore, some of the grains may not polish, or may not polish as well as other grains, preventing the achievement of a consistently polished surface. In the case of Stone 14, the surface feels smooth to my thumb but a close visual inspection shows tiny parts are unpolished. Small chips have also been dislodged from both ends of the stone.

Stone 14, polished

Detail of Stone 14, polished

Other side of Stone 14, polished

Small chips out of one end of Stone 14

Small chips out of other end of Stone 14

Tumble polishing has made the character of Stone 14 shine out clearly but it is not a perfect polish. Granite often poses this challenge for tumble polishing.

STONE 15

I observed from the outset that Stone 15 had a small gouge in the side. This gouge got progressively shallower and more smooth as the stone with through the three grit stages but remained larger than I would normally have liked when it went to the polish tumbles. However, the gouge was an indicator of the brittleness of the stone – a close inspection reveals a number of other very small cracks and chips in the stone. They were not as apparent earlier on. It is hard to know whether further tumbling with 320 grit would remove them.

Stone 15, polished. Some cracks apparent, bottom right.

Detail of Stone 15, polished.

Other side of Stone 15, polished.

Gouge in side of Stone 15, not yet completely smoothed out.

Cracks in Stone 15, polished.

The polish on Stone 15, which is probably some kind of mudstone, is not of the highest quality but again has revealed its patterns in detail.

The Seven Stages in Tumble Polishing Stones: How Stones Six to Ten Have Polished

This is the 13th Post in this series on the tumble-polishing of 40 Riverton stones, going through each Stage from stone collection on the beach through to the final polish and burnishing. The first Post in the series can be found here.

The previous Post examined how Stones 1 to 5 came through the tumble-polishing process. This Post looks at Stones 6 to 10, giving consideration to how well they have polished:

0 6-10 rough — Stones 6 to 10, rough, as collected

6-10 polished — Stones 6 to 10, after polishing

STONE 6

Stone 6 is the type of stone that shows its character only upon tumbling. When rough and dry, it is unremarkable and inauspicious. Upon smoothing and polishing, its lovely patterns and grain become clearly apparent. There are some breaks in the surface of the polished stone, including chips at one end and on both edges. In all such instances, shiny mica crystals can be seen at the bottom of the chips. I had previously noted that one of these chips occurred during the Pre-Polish tumble, and the others would have been the result of the Pro-Polish and Borax tumbles. They would have been caused when other stones bumped into this one in the barrel, even though I used a lot of plastic beads at these Stages. Tumbling again in 100, 220 and 320 grit might erase these chips but might cause others. The stone has a slightly brittle character – maybe its metamorphism was too brief to bind all the constituents together tightly.

Stone 6 polished

Close-up showing coarse grained foliation of Stone 6

At one end of Stone 6 is this chip

Under the chip in the previous photo is a cluster of small mica crystals

Another chip in the side of Stone 6

I have always felt that it is very difficult to guarantee a good smooth polish with this type of stone, though it is possible on very rare occasions and I have done it.

Stone 6 is a foliated metamorphic stone, somewhere along the schist-gneiss continuum. As a source on metamorphic rocks puts it: “Schist is a high degree of metamorphism, characterized by coarse grained foliation and/or lineation, with mica crystals large enough to be easily identified with the unaided eye. Gneiss is a medium to coarse-grained, irregularly banded rock with only poorly developed cleavage. The light and dark bands (gneissic banding) are alternations of felsic vs. mafic layers.” Based on grain size and type of banding, my guess is that Stone 6 is gneiss, while the stone below (which I recently collected on the Back Beach at Riverton and which has gone through a 320 grit tumble) is probably schist.

Probably a schist stone, just out of 320 grit tumble

Detail of stone’s grain

STONE 7

This is a gorgeous green mudstone, probably argillite, that has polished without blemish. From the wearing away of the surface, a broad light-coloured stripe has been revealed. This is in fact what is commonly referred to as a “fossilised worm cast”, left behind millions of years ago as a worm-like animal maybe crawled through mud, ingested material and then excreted it. As sediment layers have piled on top over many many years, and weight and heat built up, the process has turned mud and worm cast into rock.

Stone 7 polished, fossil worm cast apparent

Stone 7 polished.

Detail of fossil worm cast

Detail of Stone 7

Fossil worm cast stones can readily be found on Riverton beaches though they are more often associated with Gemstone Beach, near Orepuki, 30 kilometres away. (See later Posts on these types of stones and trace fossils.)

STONE 8

This green stone has also polished well, with only one small area that is not completely smooth.

Stone 8 polished.

Close-up of Stone 8.

Close-up of Stone 8

There are a lot of green stones like this on southern beaches, some of them argillite (which I don’t think this one is), many with interesting patterns in them. They usually polish well.

STONE 9

After the initial tumble in 100 grit (Stage 2), I recorded that Stone 9 had a medium sized pit in its side. After the 220 grit tumble, the pit remained. I would normally have considered discarding the stone at this point, but for the sake of this series of Posts, following these 40 stones from rough to polish, I continued with it. After the 320 grit tumble, I noted there was some smoothing out of the pit, but it remained.

Stone 9 is a breccia, a type of stone where small angular fragments of (a diversity of) rocks are cemented together in a fine-grained matrix. As John Farndon puts it on page 95 of The Complete Illustrated Guide to Rocks of the World (2012), these sharp-edged fragments were caught up in the matrix before there was any time to round off the rough edges. The pit I had noted is in effect one of these fragments sunken below the surface of the stone, probably because it is softer and has worn away more quickly than the rest of the stone (similar to Stone 4, as noted in the previous Post). However, generally speaking, most of Stone 9 has polished well:

Stone 9 polished

The main issue when polishing a breccia is whether all the various fragments will wear away at the same rate and whether they will all polish. The original pit is much shallower now but it is readily felt when a thumb is rubbed over it.

The side of Stone 9

The shallow pit on the side of Stone 9

In the course of polishing, two other fragments in the breccia have failed to polish as a result of their relative softness:

On the same side of Stone 9…

…two other fragments that have failed to polish

STONE 10

This is another breccia, and it has polished quite well.

Stone 10 polished

Detail of Stone 10

From the outset of tumbling, however, it has had a small but relatively deep hole in it, where maybe a small fragment has become dislodged. When inspecting it after the 320 grit tumble, I noticed that a couple of small indentations had also become apparent, probably where softer stone fragments had worn away a bit more quickly than the rest of the stone.

The hole in Stone 10

Two softer parts of Stone 10 that have not polished

Breccia stones are always interesting, because of the diversity of colour and shape of the embedded fragments. Many of them can be found along the southern coast.

Stones 11 to 15 are dealt with in the next Post in this series.

How Much of a Stone is Worn Away During Tumble-Polishing?

How much of a stone is worn away during any stage of the tumbling process is of course dependent on a number of factors. The three major ones are the hardness of the stone, the size of the grit/abrasive used, and the length of tumbling time.

Most of the books on stone tumbling don’t comment on this issue, though Del Fairfield in “Lapidary” (a “Teach Yourself Book” published by St Paul’s House, London, in 1973) mentions that seven days tumbling in grade 80 grit leads to “about a 5 per cent reduction” in weight (page 15).

I recently decided to pay some attention to this question so I purchased a small set of digital scales. I have done the calculations for two batches of stones so far.

The batch of Riverton Back Beach stones after tumbling in 100 grit for 6 3/4 days.

The batch of Birdlings Flat stones after tumbling in 220 grit for 5 1/2 days.

For a batch of Riverton Back Beach stones that went into a 4lb barrel and were tumbled for 6 3/4 days with 7 tablespoons of 100 grit: Starting weight of stones = 1620 grams; End weight of stones = 1424 grams. This means that 196 grams of the stones were worn away from them, which is just over 12% of their weight.

For a batch of Birdlings Flat stones that went into a 3lb barrel and were tumbled for 5 1/2 days (there was a loss of electricity which shortened the normal one week’s tumbling time) with 4 tablespoons of 220 grit: Starting weight of stones = 862 grams; End weight of stones = 820 grams. This means that 42 grams of the stones were worn away from them, which is just under 5% of their weight.

Seven Misleading Impressions from a Video Clip on Stone Tumbling

There are a number of video clips on YouTube about tumble polishing stones. This one, “The art of stone tumbling and polishing”, two minutes long, while it includes some good advice and shows the main steps involved, also conveys some misleading impressions:

1) This guy does it one-handed – you actually need both hands to do it well! (So when you make a video of it, it’s a good idea to get someone else to film you doing the demonstration.)

2) The number of stones he puts in the barrel, and the amount of water poured into it, is probably too much – most guides say fill the barrel about 2/3 to 3/4 full.

3) It’s not a good idea to let silicon carbide grit blow about in the breeze. It’s tiny and hard and sharp and you don’t want it to get into other stuff. It can do damage to a washing machine if it gets onto your clothes which are then washed.

4) He puts about one tablespoon of grit into what looks like a standard 3 pound barrel – there are different views about how much grit to use – a reasonably standard view is that you should use four tablespoons for this size barrel, some say half that, others say weigh the stones and put in a certain amount per pound of stones, and so on. You need to do your own research on this and maybe experiment with the amount.

5) “Secure lid on drum” – excellent advice, but this is not well demonstrated visually, given the one-handed approach. An insecure barrel lid is asking for disaster and the need for a clean-up.

6) “Pour off waste” after tumbling for seven days – yes, but make sure the waste does not end up down the drain where it is likely to accumulate in plumbing s-bends due to its weight and then set like concrete due to its composition! This is deemed by all leading instructors to be the most important piece of advice about tumble polishing stones.

7) “Tumble and wash each grit as before” – though sometimes you need only 3-5 days with the stage with the finest grit or a pre-polish powder, and the last stage involves a polish like tin oxide or cerium oxide.

It’s actually a great little video clip and gives me the opportunity to raise these points, all of which I am sure are well-known and appreciated by the video-maker.

How Stones Tumble in a Rotary Tumbler

Source: https://rocktumbler.com/tips/what-happens-in-a-rock-tumbler/

RockTumbler.com has a great video showing what happens inside a rotary tumbler. The clip is only 44 seconds long but it graphically demonstrates what happens if the barrel is too full and if it is not full enough. It’s conclusions are:

Barrel Too Full = No Tumbling Action

Barrel Not Full Enough = Damaged Stones

Barrel 1/2 to 2/3 Full = Great Tumbling Action

Sources of Detailed Instructions for Tumble Polishing Stones

The following are a number of sources I have found useful for the beginning (and also for the not-so-novice) rock tumbler. They share a number of things in common but also often have their own unique ideas or pieces of advice. (I will add to this List as I become aware of more sources).

1) RockTumbler.com “Rock Tumbler Instructions” – A reasonably detailed set of illustrated instructions. This site is based in USA and is the commercial site of a rock tumbler gone into business. It is noted that the owners of this site “publish what we believe is the largest library on the web of articles, videos and blog posts about tumbled stones and rock tumbling”. It is a mine of information – like stumbling upon a whole beach of colourful and already-rounded stones.

2) Alan Silverstein’s site “Collected Information on Rock Tumbling” – Sections on “Quick Start (Rotary Tumbling)” (updated 2008) and “More Detailed Advice on Rotary Tumbling” (updated 2011) – A no-frills but very informative set of instructions and advice. Alan is a software engineer from Colorado, USA.

3) Steve Hart’s book, “Modern Rock Tumbling” (first published 2008) – This whole book is full of useful information and advice on rock tumbling. The middle part of Chapter three is on “Understanding the 4-Stage Rock Tumbling Process”. Available from Steve himself and from all good online book sellers for about US$25.

4) “Professional Gemstone Tumbling” by Lortone (2011) – This is the 21-page booklet that came with my Lortone tumbler when I bought it. It is a set of basic reasonably-sound instructions, a very good starting point. I have not come across a copy of this online anywhere. Note that it is different from the “Rotary Tumbler Instructions and Parts List” that also came with the tumbler and is available online on Lortone’s website.

5) Lortone’s Instruction Videos – These consist of “How to fill a Lortone barrel” and three videos of how to change a drive belt on different Lortone tumblers.

6) “Rotary Tumbling Guide” from Aussie Lapidary Forum – A more cryptic and informal set of instructions and advice but valuable in how the author shares their rock tumbling experiences and experiments.

7) YouTube series on Rock Tumbling – Constructed by a US tumble polisher who uses his tumbler a handful of times a year, this series of six videos shows how he goes through the four stages of rock tumbling, using what looks like a 4lb barrel. The fifth video shows the resulting polished stones and the sixth video discusses what he does with his stones (he’s not into jewellery making). [Added 5 July 2019]

The Rock Tumblers…

An internet search for rock tumblers took me to the website of Rotorua Lapidary who advertised that they sold rock tumblers. So I drove over there one day and bought three machines – two Lortone Model 33B Tumblers (each of which has two 3-pound rubber barrels) and one Lortone Model 45C Tumbler (which has a 4-pound barrel).

Two Lortone 33B Tumblers (with two 3-lb barrels each)

A Lortone 45C Tumbler (with one 4-lb barrel)

I had to guess what might turn out to be appropriate for us – I thought that Petra and I could each keep one of the 33B tumblers busy, and there is the flexibility of the two barrels – and we could share the larger one. Each 3-pound barrel is about 10 cms deep and 10 cms in diameter. The 4-pound barrel is 9 cms deep and 15 cms in diameter. The “pounds” refer to the weight of the load of stones that can be placed in them – three pounds is 1.33 kgs and four pounds is 1.8 kgs.

Colin Simmons of Rotorua Lapidary told me that he started rock tumbling in 1966. He opened his shop in Rotorua in 1981 and runs it with his wife Bev. He happily spent a long time with me, answering my questions about rock tumbling and offering advice based on his extensive experience. I am very grateful for the help he provided. Along with the tumblers I bought three grades of silicon carbide grit (100, 220 and 320), tin oxide polish powder (two grades – the “pre-polish” and the “pro-polish”), and plastic pellets (which are used to cushion the tumbling stones once they get more rounded or to make up a load if there’s not enough stones for the barrel). I was now ready to set up a small stone tumbling operation!