Category: Information Sources

Putting plastic pellets into a tumbling barrel.

The pellets are stored according to the type of grit or polish used, to avoid cross-contamination.

Cover of Lortone’s instruction booklet.

Pages 8 and 9 of Lortone’s instruction booklet.

One of the issues facing rotary tumble polishers like myself is the use of “media” in a barrel. As RockTumbler.com puts it: Tumbling media has four functions: 1) it delivers grit to hard-to-reach rock surfaces; 2) it is used to cushion fragile rock materials during the tumbling process; 3) it is used to improve the tumbling action in the tumbler barrel; and 4) it is used as a filler to make up for lost [or inadequate] volume. An instruction booklet that comes with Lortone tumblers, “Professional Gemstone Tumbling”, refers on page 8 only to the use of plastic pellets as an option that can be considered, especially during the latter two stages of tumbling (see photos above right). My supplier, Rotorua Lapidary, stocks plastic pellets and offers them as an integral part of tumble polishing (see here). I have incorporated them into my tumbling routine, always using a few even with coarse grit, increasing the number with each stage. Item 8 in my Posts on What Do I Need to Start Tumble Polishing Stones Myself? And What Will It Cost Me? explains my use and storage of plastic pellets. I am very careful not to lose pellets down the drain when rinsing stones from the barrel, assiduously checking for them even where the water drains onto the ground outside my tumbling shed. However, once I became aware that tumbling especially with coarser grit actually wears away the pellets, no doubt releasing microscopic bits of plastic into the environment, I started to have second thoughts. I would like to minimise the amount of plastic I am responsible for in the environment. The following is my initial research into alternative tumbling media, looking at the advice and information given by various sources.

Hart, top half of page 29, on plastic pellets.

Hart, bottom half of page 29, on plastic pellets.

Some of the ceramic shapes I bought from The Little Red Store.

Hart, top of page 22, photos of ceramic media.

Hart, bottom of page 22, photos of ceramic media.

Hart, top of page 58, on ceramic media.

Hart, bottom of page 58, on ceramic media.

A good starting point for research on any tumble polishing matter is Steve Hart’s “Modern Rock Tumbling”, published in the USA in 2008, what I have called “the best rock tumbling book around”. Hart mentions the use of plastic pellets but states that he prefers ceramic media (see photos above). [He also notes that if he does use plastic pellets, it tends to be mainly for the later stages of tumbling, and he uses them only once before relegating them for use at earlier stages.] On pages 27-28, Hart writes: I have learned to use non-abrasive ceramic shapes in assorted sizes in order to make up for any errors in making up the “perfect” assortment of sizes and to act as a cushion for brittle batches. Use 1 to 2 tablespoons of ceramic shapes for every pound of rocks to start – then make up for lost volume with the shapes [if necessary]. I bought some of Hart’s ceramic shapes in 2016 from his Little Red Store located in California. I used them on a 320 grit load but thought they might have damaged a couple of stones. So I set them aside and have not yet come back to them, partly because the plastic pellets work so well. I have seen comments on the Facebook Group “New Zealand Lapidary, Rocks, Minerals, Fossils” by people who have found ceramic media to work effectively for them.

One rock tumbling retailer in the US, who runs the RockTumbler.com website, summarises the use of plastic pellets versus ceramic media here in the following way: Plastic pellets were the most popular tumbling media from the 1960s through the 1990s. They were used to cushion the stones and reduce bruising caused during tumbling. Today most people use ceramic media, but some have used plastic pellets for decades and still prefer them for rotary tumbling. Ceramic cylinders smooth the tumbling action and this results in less bruising of the stones. Ceramic media is also hard and more effective at grinding and shaping stones. When ceramic media became popular in the early 2000s, most people who tried it stopped using plastic media – because ceramics were more convenient. When using plastic pellets, the pellets can only be used with one size of grit – because tiny particles of grit become embedded within them. When using ceramic pellets, the rock mud and the grit rinse right off of the stones between tumbling steps. Here is the verdict of our customers: Today we sell over 10 times more ceramic media than plastic media. One way to expand our knowledge of the alternatives to plastic pellets is to ask, What did tumble polishers use before plastic pellets? It is worth consulting older literature for the answer.

Page 56 of Lyn & Ray Cooper (1966).

Page 126 of Natalie Fernandez (1981).

Mainly in the first year of my tumble polishing, I managed to buy a few older books on tumble polishing, primarily from Great Britain, the United States and New Zealand. The following three paragraphs summarise the kind of advice given in some of them. Firstly, two New Zealand books: Lyn and Ray Cooper’s (1966) “New Zealand Gemstones” does not mention tumbling media when going through the various stages, though noting that smaller stones can be used as fillers. When discussing how to tumble softer stones, their section on obsidian states (pages 55-56): The polish consists of 2 lb of tin oxide, 1 lb of sugar and 1 cup of Rinso to each 10 lb of stones… Various overseas publications suggest the use of fillers such as plastic pellets for obsidian and soft stones; we do not recommend them. We have used plastic pellets and found that our Rinso and sugar additives give exactly the same, if not better results. Natalie Fernandez (1981), in “The New Zealand Rockhound”, also mentions “hard small beach stones” as a filler (page 126). On the same page, when discussing the polishing stage, she writes: Suitable fillers if required at this stage are saw-dust, shavings, rubber strips, even walnut shells and kitty litter. She goes on to add a note about role of sugar: Adding a little sugar slightly thickens the mixture which keeps the polishing material in suspension.

Fletcher (1972), page 69.

Fairfield (1973), page 16.

Firsoff & Firsoff (1975), page 181.

Shore (1978), page 84.

Next, to look at four British books (see photos above). In “Pebble Polishing” (1972), Edward Fletcher does not mention tumbling media when he provides instructions for the various stages of tumbling. However, for the polish stage, he mentions on page 69 that “wallpaper adhesive” can be used to prevent the cracking and scratching of stones when “any harsh banging or unrhythmical striking of pebbles together” is heard: Add a small amount of wallpaper adhesive to the mixture. The aim is to thicken the liquid in the barrel so that it cushions the fall of each pebble. Do not make the mixture too thick, otherwise the effectiveness of the polishing agent could be reduced. A thin cream consistency is ideal…It also increases the time you must allow for the polish to do its work because movement inside the barrel is reduced owing to the greater viscosity of the thickened liquid. A polishing stage of four days without paste might take seven days if paste is added. Secondly, Del Fairfield’s (1973) “Lapidary” mentions quite a range of tumbling media though for use only at the polish stage: It is customary to add a quantity of soft material to the barrel to provide cushioning during the polishing process and also to carry the polishing material. Various materials have their advocates, including leather, wood, hardboard, plastic granules, cork crumbs etc. Leather, for instance, should be heavy soling leather cut into 1/2-inch squares, and wood should be in 1/2-inch cubes. This additional material should be about one-third the volume of the stones, and when stones, cushions and slurry [tin oxide or cerium oxide] are all mixed up there should be an adequate coating over everything but not much spare slurry (page 16). Thirdly, V.A. Firsoff and G.I. Firsoff, in “The Rockhound’s Handbook” (1975), also recommend the use of “small pea-sized stones” which “ensure more intimate contact between the main charge [stones] and the abrasive” (page 181). They mention the use of “vermiculite” to cushion the stones at the polishing stage (page 182). Vermiculite is a hydrous phyllosilicate mineral (see Wikipedia), a mica-like mineral, and one of its commercial uses is as an addition to potting soil in containers, helping to improve drainage and moisture retention. Finally, Eric Shore includes the following comments in his “Lapidary for Pleasure and Profit” (1978) when discussing the polish stage: Additives either of cubes of hardwood, pieces of felt, or leather should be added to the charge [stones, polish powder and water] to give a cushioning effect whilst tumbling. These will help prevent chipping 0f sharper edges and points and also act as a polisher when rubbing against the stones. If leather is used, thick pieces are better than thin, as the latter tend to cling to the barrel and not mix with the stones (page 84). He also mentions that sawdust can be used, along with detergent, in the final burnish.

James (1965), page 97.

Hyde & Matthews (1977), page 33.

Hyde & Matthews (1977), page 34.

An Australian book published in 1965, Bill James “Collecting Australian Gemstones”, actually mentions “plastic granules” to prevent damage during polishing for “special” stones (page 97), but is silent on tumbling media for the routine stages for most stones (see photos above). A book published in the USA in 1977 mentions tumbling media, and gives mainly similar advice to the British authors reviewed above. “The Complete Book of Rock Tumbling” by Christopher Hyde and Richard Matthews has a section on “Buffering Agents”: These are used to carry the abrasive and also to prevent severe impact of one stone against the other… Such materials include wood chips, plastic pellets, sawdust, sugar and wallpaper paste… Old-timers often had their own favorite additives, which helped to make rock tumbling a mysterious art. These included products such as walnut shells, rice hulls and even banana peels. Although such things may work, we don’t recommend using them (pages 33-34).

In Part Two in this Series (not yet available), I will review some contemporary internet information on tumbling media.