Tips for Polishing Turquoise
Tips for Tumbling Turquoise
Polishing turquoise in a rock tumbler is challenging and it can grind away more valuable rough than cutting it by hand. However, some people get good results if they begin with good material and clean the rough and tumbler barrel/bowl thoroughly between tumbling steps. Here are a few thoughts on tumbling turquoise that might be helpful. If you are not familiar with turquoise you might want to read an article about it here before you begin.
Matrix Can Cause Problems
Some turquoise has a gritty matrix or contains embedded particles of quartz or country rock. In the tumbler these foreign particles can stand up in positive relief and scratch every other piece of turquoise that they come in contact with. These pieces of turquoise might also shed the foreign particles during the fine grit and polish steps in the tumbler. These stray particles can ruin the polish of every other stone in the barre.
These problems can be reduced by carefully examining your rough before tumbling and removing the pieces that might cause a problem. One problem piece can ruin an entire batch of tumbled stones.
You can sometimes polish turquoise with problem matrix. Try it by tumbling as normal during the first grind, then, during the fine and polishing steps, fill the barrel almost to capacity with ceramic media, then add water and abrasive. Then add a small amount of turquoise. This allows the turquoise to be lost in a "sea of ceramics". In that sea, problem pieces of turquoise and stray particles of quartz or country rock will have fewer scratch-producing contacts with other pieces of turquoise. Do not run any longer than needed to minimize scratching.
Soft Material Disappears
Turquoise is said to have a hardness of 5 to 6 on the Mohs Scale. However, turquoise that has been in or near the weathering zone might be a lot softer. These soft spots will quickly be chewed away in a rock tumbler. This soft turquise is not worth tumbling.
If you are tumbling sound turquoise will still be a lot softer than the typical agate and jasper that most people tumble. Many people who tumble turquoise skip the coarse grit step of standard rock tumbling instructions. They start tumbling with medium grit. Before tumbling check your turquoise for soft spots with a sharp steel nail. Nails have about the same hardness as good turquoise. Turquoise that can easily be pierced or scratched with a nail is probably soft and will be rapidly abraded to mud in a tumbler.
Why Most Turquoise Tumbling Fails
Most people who have cabbing grade turquoise will cab it. Most people who have turquoise that is not nice enough to cab hate to throw it away. So, they decide to run it in a tumbler. Most turquoise that falls short of cabbing grade will not perform well in a rock tumbler. The exceptions are: really nice pieces that are too small to easily cab and pieces that don't have color that motivates a person to spend time cabbing. These exception pieces can produce nice tumbled stones. If you have a lot of small pieces that are chunky but too small to cab, begin with fine grit or add them to a batch of other tumbled stones at the beginning of the fine grit step. For sound, but less-than-top-color turquoise, use our standard rock tumbling instructions and start with the medium grit step, running it for just four or five days.
Grinding For Best Results
Before you place anything in a tumbler, examine your rough. If it has odd protrusions, voids, attached country rock, gritty matrix or other irregularities, consider spending a few minutes at a lapidary grinder with a water spray. Grinding these flawed areas against a diamond or silicon carbide wheel for just a moment will sometimes grind away problems and help you produce tumbled stones with more attractive shapes. This is really a good use of your time and your rough. Turquoise is a lot softer than agate or jasper so the amount of grinding needed to work out a problem spot is usually very small.
If you are used to tumbling agate, jasper, chalcedony and similar materials with a hardness of 7, you might be surprised at how quickly turquoise grinds away in a rock tumbler. Tumbling that would normally require a week for agate and jasper might only require two to four days for turquoise. Small pieces can disappear overnight ! It is best to check turquoise frequently to be sure that you are not grinding valuable material into mud.
Overtumbling during the polishing step should be avoided. Stop tumbling as soon as you have a satisfactory polish to avoid the risk of scratches and broken stones. Running turquoise in a vibratory tumbler during the polishing step allows you to quickly and easily remove the lid, check the polishing process and stop it as soon as a good shine has developed.
Sort, Grind, Observe, Experiment
All of the tips listed above recommend sorting, grinding, observing. Then, to optimize your results, modify your procedure with a little experimentation. Your first attempts should be with small batches of less desireable material. Use these first attempts to gain experience before you risk a lot of material or your nicest material. Those are the keys to producing nice tumble turquoise. Experiments take time but you are working with rough that can have a much higher value than the typical agate or jasper.
Also, keep in mind that turquoise is a highly variable material. It varies by hardness from one part of a single deposit to another. It varies in the amount and type of matrix in the stone. For these reasons it is impossible to give "standard turquoise tumbling instructions". You must tumble some material, learn how it behaves and adjust your methods accordingly.
Ceramic Media Highly Recommended
Any time we are tumbling fragile material, valuable material, or when we want to do the best possible job, we add ceramic media to the tumbler barrel. The ceramic media acts like roller bearings and gives the rocks in the barrel a much gentler ride and much more thorough smoothing. It can also be used as filler. If you are experimenting with turquoise, consider running a barrel full of small ceramic media, or a mix of small and large ceramic media, with just a few pieces of turquoise. If you get great results, increase the amount of turquoise next time. If you get poor results, you didn't waste a whole barrel. Then adjust your tumbling time, your pregrind time, your starting grit size or your media ratio, based upon what you learned from tumbling the first batch. Tumble larger batches after you learn how your turquoise behaves.
Article Authored by
|Bradley Cole: Bradley is the manager of RockTumbler.com and has authored much of the content on this website. He also does customer support, photography, maintains the website, and consults with customers about rock tumbler repair and maintenance.|
|Hobart M. King: Hobart is the owner of RockTumbler.com and has authored much of the content on this website. He has a PhD in geology and is a GIA graduate gemologist. He also writes most of the content for Geology.com.|