Home >> Hobbies >> Gemology

How to Lap a Stone

Lapping a stone is a method of grinding away at a stone's surface with an abrasive covered moving plate, flattening the surface. Used correctly, lapping creates facets in stones, shaping and polishing the stone into beautiful gems in the process. With time, a lapping plate can grind away any stones allowing its use to shape even the hardest gemstones.

Things You'll Need

Lapping machine
Cloth
Acetone
Polishing powder or paste
Dop
Hot wax glue
Stone
Isopropyl alcohol

Instructions

- 1
  Prepare the lap base plate by removing any glazing from its surface with 120-grit sandpaper. Attach the sandpaper to a wooden block. Sand the surface of the plate lightly until you've scraped away any shine from the plate. Wipe the plate with a cloth dipped in acetone to remove any sanding residue and wait five minutes for the acetone to evaporate.
- 2
  Apply a polishing powder, such as aluminum oxide or polishing paste to the plate. Use a plastic spatula to spread the material over the plate evenly until you have a thin film across the entire plate surface.
- 3
  Glue the stone to a small peg known as a dop so that you can hold the stone against the lap plate. Use hot wax glue on the side of the stone directly opposite that you wish to facet and then press the stone firmly to the end of the dop until the glue sets.
- 4
  Start the lap plate rotating. There is no set speed for lapping a stone, but you don't want to go much higher than 600 rpms as this could cause the stone to cut too quickly or cause furrows in the stone due to one section of your lap plate having slightly more polish on it that other sections.
- 5
  Press the dop to the lap plate and hold it at the angle that gives you the faceting on the stone desired. The plate grinds away at the stone surface, flattening the stone where it touches the plate. Use a moderate level of pressure to get a consisting grinding of the stone surface. Increase the pressure to grind the surface down faster.
- 6
  Remove and examine the stone for effect. If scratching occurs, turn off the plate and wipe some of the polish from the surface with a piece of tissue. If scratching continues, remove the polish by wiping the pad with an alcohol-dampened cloth, and then reapply the polish in a light film.
- 7
  Adjust the stone's position on the dop to polish a new face by heating the wax then shifting the stone in place. Allow the wax to set then polish the new stone face. Recharge the surface of the plate when the polish begins to wear off, and then continue faceting the stone until you have the shape desired.

Gemology