For once here is something in the gem world that makes total sense! A “lap” is a horizontal rotating disc that Lapidarists use to facet and polish gemstones. In most cutting houses across Asia, Lapidarists choose to sit on the floor and the “lap” is literally spinning in their lap! Hooray – something easy to remember at last!
But now it gets a little more complex. In nearly every book you read that introduces you to gemstone cutting, to communicate the process in an easy to understand method you only ever hear of metal wheels and diamond paste. However, the art of Lapidary is more than just developing the skill of knowing how to orientate the first cut and how to angle and arrange the facets, it is also about knowing which tools to use for shaping different types of gemstones.
When it comes to the lap itself, not only is the choice of material significant - plastic, brass, copper, lead and tin all work differently with different gems – but even the finish on the lap (for example, how highly it is polished) makes a difference. Then the polishing compounds and various pastes all have different effects on these different laps. To put this into context, in our cutting house in Jaipur, we estimate that there are over 200 different combinations of laps and pastes used to facet and polish different gems! Even though you can give guidance to your Lapidarist, as this is an art and not a process, in the end the choice of tools comes down to the individual’s experience and preference.
Here are a few of the most regularly used combinations in our cutting house: Brass laps and Diamond pastes are used to facet Sapphires and Rubies; Copper laps and Diamond powder for Topaz and Quartz; Lead laps used in conjunction with tin oxide or chromium oxide polishing powders are popular for cutting Emeralds (a combination created in Jaipur over 200 years ago); Tin laps are used for polishing a variety of gemstones including Beryls, Garnets and Tourmalines (however, with some gem varieties tin is considered too soft and a tiny amount of antimony is added to harden the lap). Tin laps work with a variety of pastes including tin oxide, alumina powders and Diamond.
