Jewelry, Gems, & Minerals/kyanite
QUESTION: Is it possible to buff out a scratch on a Kyanite cabochon or will it only get worse? I've got a slant cabber machine but I do not want to try it willy nilly. It's a 1 carat cab, set in sterling silver with platinum overlay and it has Iolite rounds next to it on both sides. This ring did not cost me much but I really like it and really wish I'd read the Mohs scale on it BEFORE I started wearing it around. Thanks in advance for any advice.
ANSWER: Dear Ellen,
The interesting characteristic of kyanite is its double hardness. In one direction on the crystal you see a relatively soft gem around 5 on the MOHS scale and nearing 7 MOHS in the other direction. Of course, in a cabochon, it is hard to know which way is which!
In polishing out a scratch, consider the depth of the scratch. Of course, enough material must be removed to cut below the deepest part of the scratch while maintaining the domed form of the cabochon. Is the damage at a location which allows you to work the cabochon while still mounted in the ring? That would avoid risk associated with removing the gem from the setting to polish then resetting the stone. You do not want the sanding disks to cut the metal or to contact the iolite stones.
Considering the variable hardness of kyanite, I would not use anything but diamond for polishing. A linde® powder or tin oxide might work but diamond seems to do best with variable hardness in gems. Lapis and jades can be a pain but diamond make it go well. This should work fine with kyanite. A final grit might be about 14000, or 1 micron. I don't believe going finer will be necessary.
Keep the stone cool and wet while working it and go at a medium speed, not fast enough that you look and discover a flat spot or that you have cut away too much. This is most important at coarser abrasive sizes. If the scratch is not very deep, you might get away with starting at 600 grit which will cut slowly enough to be more controllable.
Ellen, I can be done. The problem is having experience using kyanite on a cabber machine. You really do not want to learn your mistakes on your ring stone! That is why I suggest going quite slowly to start.
It was done to start when your stone was cut and should be able to be done now. Do yourself a favor before starting and use a small flashlight or light at the "edge of a lampshade" to look into or through the stone. (You can hold the stone at the shade edge and block the main light, allowing just enough to lighten the stone interior.) The idea is to be sure the scratch is just that and not the top of a fracture which goes into the gem. If it is a fracture, I advise against trying to polish it because in that case it could get worse in the process.
Best wishes. God Bless and Peace. Thomas.
[an error occurred while processing this directive]---------- FOLLOW-UP ----------
QUESTION: Ok, I will try looking at it with a light before I try anything. I attached a picture but it might be too small to show the scratch. I saved your answer so I will get the right diamond polish. Thank you very much for your help
I changed the contrast a little to help me see the ring better and ask a question: Is the light colored line right on top of the cab the scratch? Is it deep or shallow and wide? If deep, more careful sanding will need to be done with the stone constantly moving to maintain the domed shape.
Do you feel comfortable removing the stone from the ring? If not, you might have a jeweler do that for you. Removal and resetting should be relatively easy with the 4 prongs. The jeweler needs to know you are going to polish the top of the stone and then have it reset in the ring mounting. This way, an effort is made not to damage the prongs in the process.
Likely the polishing can be done without removing the kyanite but I believe having it on a dop stick by itself will allow a much more uniform polishing. You need to definitely avoid going down the sides of the stone to the bottom girdle(waist) of the stone. The stone will be slightly lower when finished but the oval of the base should not be altered so all will reset neatly into the ring.
A suggestion to help avoid sanding too far down the stone and changing the oval shape of the bottom: Take Whitout™(not water soluble but the solvent type) and paint a little line on the outside of the stone just above the edge of the base. While polishing, you can see this line and know where to stop. The line may be removed with acetone(or acetone nail polish remover) or strong alcohol.
Dop stick for a heat sensitive stone: You need a DOP stick of wood or the aluminum sort that sometimes come with cabbing machines and some dop wax and superglue. Put wax enough on the stick to spread out to cover the stone bottom and support it on the stick end. Heat the wax gently to make it pliable. Put as drop of glue on the stone bottom and quickly press into the soft wax. The wax needs to be warm enough to move to finger pressure but not hot. The idea is to secure the stone to the dop stick without getting it hot. Once pressed into the wax on the end of the stick, form the wax below the stone neatly to avoid the edge of the base yet provide support. Set aside for a moment then check to see if it is tight.
This method of holding the stone to the stick for polishing is not as strong as heating both stone and wax but it does prevent heat shock damage to the stone. As you are at the cabbing machine, use gentle pressure and check the stone often to be sure it is tight on the wax. You might put a small wash cloth or similar item as a cushion should the stone come off. This is not to frighten you because the stone will most likely stay firm and secure. But...precautions are always a good idea.
An flat and sharp razor blade may be used to chip away wax from the stick to remove the stone or if the stick is aluminum, heat the stick away from the stone so the wax may be pulled off the stick. Remaining wax on the stone will dissolve in denatured alcohol and if needed, the super glue will come off with acetone or maybe with a gentle fingernail try.
Ellen, this should go ok for you. God Bless and Joy to All. Thomas.