Abrasion Theory And Application

Achieving a polish on stone is largely a product of our human vision, our ability, or inability, to see beyond a certain level of abrasion. After an initial PRIMARY abrasive application to most materials, these materials appear frosty, with a dull matte look. This is because the heavier, lower numbered silicon carbide abrasives (100-220), which are harder than most materials, visibly scratch the exterior of the rock (Abrasion). And because this scratching is relatively large sized, our eyes perceive the surface of the rock as being only somewhat uniform, giving it a frosty appearance. As the numbers of the polishing grits increase though, the size of the grit particles become smaller and smaller (As in so-many particles per cm) until we reach the final stages where the grits appear almost flour-like, very fine. Those abrasives work just as well, if not better than the heavier sized abrasives, once the heavier abrasives have begun constructing UNIFORMITY. The later grades of polishing abrasives make scratches so fine on a gems exterior that our eyes can no longer perceive the abrasions as scratches (That frosty look) and what we see is a smooth and shiny surface created by millions of tiny abrasions which allow light to travel more efficiently across or through the material of the stone. So. Polishing rox is a matter of Abrasion and Vision and Light. You are controlling, refining, the way Light effects a material, by altering its surface through uniformity (Smoothing the surface by gradually SCRATCHING it more finely) to allow Light better access, so that your eyes can no longer perceive the scratched look of the stone, for the watching of the Light! Many types of finishing on materials is called polishing, and that can basically be understood as “High Surface Uniformity”. Polishing is Abrasion. Machinery Parts, and the like, can easily be made more inherent, have higher synchronous capabilities, through polishing. Many abrasives are applied with water, although dry abrasion is very effective too in certain instances. Mixtures of wet and dry abrasion create their own interesting effects, and experimentation is yours. Experimentation is what its all about. Trix. Dry abrasion generates heat at a much higher rate, and this needs to be understood. A safety hazard is many times created during dry grinding or sanding, too. Airborne particles, inhalable. Remember that first and foremost. Fans work well to blow particles somewhere else, away from you, and dust masks are necessary if you get into dry abrasion at all.
As a rule, for lapidary work, you want what is called an abrasive slurry while working surface on surface, such as cabochon against the wheel, or rough rox in the tumbler. A slurry is a mixture of water and abrasive grit, which can range from fluid to paste. Pastes are to be avoided during tumbling (Add water) but pastes are desirable for a lot of wheel work. Judge the amount of abrasive-to-water by the job it does on any given material. If the material is not polishing fast enough, you may very well need to add more abrasive, but that is rarely the case, because a lot of abrasive goes a long way. Make sure your abrasive is “Carried” effectively to the surface you are polishing, and study the characteristics of the particular abrasive, to be sure it is apt. The development of material uniformity is a progression. From coarse to fine a material is “Sanded”. The measurement of the size of an abrasive grit is actually judged on the size of the particles, for the most part. So-many particles per whatever, like particles per square millimeter. This means the finer stuff has the higher numbers of course. Remember too, abrasives do break down as they are used, they become worn, which is part of their purpose. Sometimes broken grits of heavier material can be salvaged and employed farther down the line, or at another time. Many trix. Many rox. Application of abrasive runs from permanent (Plated diamond on a wheel) to simply mixing with water. Pastes can be applied to wheels with brushes safely, and of course with tumblers cover your rox with water then start with perhaps 1/4 to 1/2 cup of abrasive per 10 pounds of material. Again, experimentation will clue you to the most efficient process for your situation, and you will get better, fast, at learning the ins and outs of abrasion. Silicon Carbide is very good to work most rox, and is cheap. Diamond is a dream, but more expensive. Some powders can be salvaged right from nature, out of streams and rivers when the water level is low.  Research the phenomenon of  AGGREGATION. 

 

 There are a plethora of rock shops online selling abrasive in small quantities. Larger quantities can be gotten at wholesale abrasive suppliers like 3M. I polish by hand on either flat laps or drums, with 100 grit, then 220, then 400 silicon carbide. Any higher you go with that the better, but after about 600 the noticeable effect will be nominal. I then go right to cerium oxide and work it a little dry. I get a mirror-like finish on my surfaces this way. In tumblers many folks like to use cushioning agents in the final polish, like plastic pellets, but truthfully I do not use the tumbler much to do final polishing. I use my tumbler to grind and sand preformed cabochons or beads, and then finish-polish on a wheel. I have used pellets in the final phases of tumbler polishing occasionally, but most times not, and both methods have worked for me. If the stuff you are tumbling is very fragile, pellets are recommended. Finally, contamination is always a problem to be reckoned with. That means that some rougher abrasive gets in with the fine stuff. This needs to be avoided at all costs. And it will STILL happen occasionally. In the tumbler you must thoroughly wash between each stage, both the rox and the tub. Check the rox real good because grit lixes to hide in the crax, and will sometimes deposit in the crax of the rox as a byproduct of tumbling axion. Eeeshk.