“What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me?” Part One of a Two Part Post

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 Grit sells 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.]

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.

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)

NOTE: You can get a sense of all the elements and equipment involved in tumbling a batch of stones in this post describing the details of the various stages in doing a 100 grit tumble.

5) MEANS FOR DISPOSAL OF SLURRY

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.

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 

TOTAL so far = NZ$574.95 (plus postage)

Continued in Part Two.