Articles

Duncan Miller

Initial dopping requires a flat surface on your rough. Prepare a flat dop with a blob of hot wax on it and in the transfer fixture push this against another flat dop face to form a layer of wax a few millimetres thick. You can build this up with several layers if the stone you are going to cut is very heat sensitive. Clean the flat on your rough with alcohol. When the wax is cold, apply a small drop of cyanoacrylate glue (CA), position the rough on the dop quickly, and let the glue set. Paint the join with clear nail varnish to protect the CA bond from softening in water. Then cut the pavilion.

There are two ways to do the transfer. If the stone is not very heat sensitive, fill the pavilion dop with wax and let it cool until it is still just plastic and takes a dent from a fingernail. Then push the pavilion into it, in a transfer fixture of course, and pull it out again quickly to make an impression of the pavilion. Use a small amount of CA in the impression to glue the pavilion to the wax. Using a CA accelerator, like Zip Kicker by ZAP, helps set the glue if it is reluctant. When the CA has set, paint the join with clear nail varnish. To remove the initial dop, hold the stone itself between your fingers, heat the stem of the initial dop, and with a twisting motion detach it as soon as the wax layer is soft enough to release it. You can scrap the surplus cold wax off the stone with a blade.

For very heat sensitive stones, the alternative is to make yourself a set of 'anti-dops' (see picture left) by grinding large cylindrical dops into a 45° cone, a wedge, and a trigonal pyramid on a coarse lap. (I owe this idea to Tom Herbst's Amateur Gemstone Faceting.) Use an appropriate one of these in the transfer fixture to make an impression in soft, low temperature wax, like jeweller’s green wax. When it has cooled you can glue a heat sensitive stone into that impression, preferably using a gap-filling CA and accelerator, followed by the clear nail varnish treatment. Remove the initial dop as described above, without allowing the stone to heat up at all. After cutting the crown, soaking the stone and dop in acetone overnight will result in a clean stone. (Gap-filling CA and Zip Kicker are available from hobby shops selling model kits.)

See also

https://www.gia.edu/gems-gemology/optimizing-face-up-appearance-in-colored-gemstone-faceting