What is a Last Lap and how do I use it?
Last Laps are made by Crystalite. They are a modern pellet type of composite surface that is designed for polishing gem stones. They usually come (new) with a little container of 50,000 diamond polish suspended in extender fluid. Like a lot of other types of polishing laps some people like them and some do not. I am neutral on them, they worked for me but I think other laps are better.
I have had mixed results using them and found that they work pretty well for polishing most materials. The main drawback to them as far as I am concerned is that they heat up your stone during polishing and they do not polish all that fast.
But they do work pretty well and if you are cutting a lot of man-made materials (like Sapphire, Spinel…) you might find one or two (a pre-polish and polish) very useful. It depends on how you cut and what you like really.
Follow the instructions to charge your lap. A Last Lap can be used with about any diamond polish grit/size, 8,000, 14,000, 50,000, 100,000.
It usually just takes 2-4 dabs of the diamond and extender fluid mixture, gently worked into the last lap using a clean finger. Last Laps do need to be lubricated, do not run them with water or dry.
Use Crystal Lube or some other oil based lubricant. Run them at a moderately slow speed (this will help reduce the heat build up on the stone) and gently sweep the lap with the stone/facet. Because the extender fluid has an oil base be sure and wipe your facet(s) carefully and examine them closely for scratches.
Sometimes the oil/polish is hard to get off of the facet for a good look. I use a wipe with a little alcohol on it once and a while to clean the stone so I can really see the facets. Be careful with alcohol around your dopped stone if you are using wax, alcohol will melt the wax eventually.
If the lap becomes contaminated gently wash it with a mild dish soap and warm water. Like most laps that you use with diamond polish, a little bit goes a long way. Do not over charge the lap.
If you do over charge the lap you will often get scratches from the diamond polish balling up and rolling across the lap. If this happens clean it with a wipe and a little alcohol, use alcohol sparingly, too much is not good for the lap. Lightly recharge the lap with diamond polish and continue.