A Faceting Breakthrough FOR Corundum, CZ and Spinel on Ceramic in Conjunction with a New Acid Solution

by Dr. Tom Gray – edited by Charles Moon, United States Faceters Guild

Dr. Tom Gray, master of sapphire faceting, design and polishing thereof, has what he feels is a BREAKTHROUGH in polishing sizable sapphires, smaller sapphires in the 1/2 carat to 3mm size and softer stones, e.g., CZ and spinel.

Tom is one of those rare faceters who has positive results with ceramic laps. His article, “Tips on Ceramic Use and a New Method for Cutting and Polishing Tables” appeared in the USFG Newsletter, page 11, Dec. 95.

Tom’s BREAKTHROUGH came via the addition of acids to his water drip. He started off by using the familiar 5% vinegar solution, but after discovering Sodium Bisulfate, a dry-acid-pH decreaser used in swimming pools, he now prefers a 5% solution of the Sodium Bisulfate. The “S.B.” solution seems to work better than vinegar and does not have that vinegary smell. A 5% solution is accomplished by adding 4/5ths of a teaspoon of Sodium Bisulfate to 100cc of water. N.B. The solution does not affect the hands or ceramic laps, but please note, it is not recommended for metal laps.

The manner in which Tom charges his ceramic is most unusual. He first dabs the 8000 Vaseline-diamond paste on a single facet, makes contact with the ceramic, wipes facet with finger, then puts the diamond paste back onto the lap. This practice continues, and quote, “if one desires, one can always add a little 8000 spray, but really isn’t necessary.”

About one drop of the acidic solution every 15 seconds, that’s the time frame. The slow drip supplies a “damp-dry” condition — neither damp nor dry. It’s the lap condition plus the acidic solution that expedites the pre-polish and polishing stages. The acidic drip is used in all pre-polishing stages for large/small corundum, CZ and spinel. N.B., The acidic drip is optional for polishing with 100,000, but is mandatory for polishing with 200,000.

PROCEDURES: Lap revolution is always about 1/4 motor speed. Pre-polish and polishing is always accomplished on a ceramic with a sweeping motion.

  1. For pre-polishing corundum larger than 1/2 carat, Tom goes from a 600 metal lap to a ceramic charged with 8000-Vaseline paste, and applies the acidic drip. It is important to note that he bypasses the 1200 metal lap, which can induce the inherent “sins” of corundum, i.e., glazing, pitting and tearing.
    1. For a super polish of ‘1’ above, he sprays a freshly scrubbed ceramic(see 3rd paragraph from the end) with 1/4 micron (100,000), allows it dry, finds his facet, then expects the super polish with no more than two passes. N.B. Quote, “The acidic drip is optional, but does expedite the polishing.”
  2. Another breakthrough is his being able to polish most successfully with 200,000 spray. Credit is given to the use of the acidic solution, which is applied for both pre-polish and polish stages. Pre-polishing is done on the 8000 ceramic; polishing is done on a 200,000 ceramic. The 200,000 is sprayed on a couple of times and allowed to dry before the acidic drip is applied. {Tom mixes his own spray — diamond bort in alcohol.)
  3. Since it is often difficult to facet small stones under 1/2 CT. on a worn 600 metal lap, Tom has solved the problem by cutting on a copper lap charged with 800 bort. Pre-polishing and polishing are carried out as above.
  4. For CZ and spinel, pre-polish is achieved on a well worn 1200 metal with a H2O drip; polish is achieved by going directly to 100,000 spray on ceramic, let it dry, apply the acidic drip, then polish.

Ceramic Laps: Used on both sides — one for corundum and the other for softer stones.

If a used ceramic lap is available and has an unknown diamond grit on it, or is somewhat worn, it must be reconditioned. Tom hand laps a ceramic on a piece of flat glass with 220, 400 and 600 silicon carbide grit, washes after each grit; finally, scrubs well with a stiff brush, detergent and kitchen scouring cleanser; then if necessary, gets rid of possible silicon carbide remnants by scraping with a piece of corundum — washes thoroughly before charging. Quote, “It’s a long process, because you really have to work on it.”

The visual condition of the ceramic after each 220/400/600 lapping is very much like the visual condition of a piece of jade or jasper after grinding and sanding with the same grits.

If the ceramic begins to scratch, immediately scrub the lap well with a stiff brush, detergent and kitchen scouring cleanser, wash thoroughly, then continue with polishing. This pristine condition of the ceramic is a “must”, particularly if one is going to do a larger facet, e.g., a table. And it is also a “must”, if one has to cut a softer stone on the same side that a piece of corundum has been cut.

The following is a reply to a question as to how he breaks in a new ceramic: quote, “I just start right out polishing, and this seems to do it, especially after one or two stones. I have not had to do any special breaking-in procedure on the two main types of ceramic laps, but there may be some that need it.

In closing, Tom Gray hopes that all of the above ideas and suggestions will make faceting rewarding, fulfilling and fun for all faceters especially for those who have idle ceramics sitting around.

Tom Gray, MD, G, is the former Director of Health Service at San Jose University, San Jose, CA. The above article came from Dr. Tom Gray via the telephone and mail.

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