Tips for Polishing Turquoise
Tips for Tumbling Turquoise
Polishing turquoise in a rock tumbler is challenging, but 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.
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 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 in coarse and medium grit. 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. 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 scratched with a nail is probably soft and will be rapidly abraded 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 or too thin 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.
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 wheel for just a moment will sometimes grind away problems and help you produce tumbled stones with attractive shapes. 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
All of the tips listed above recommend sorting, grinding or observing. Those are the keys to producing nice tumble turquoise. These take a little time but you are working with rough that can have a much higher value than the typical agate or jasper.