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ALEXANDRITE : Anita, I've never used synthetic alexandrite fired in PMC, but you should nothave any problems. Synthetic Alexandrite can be cast, stone in place, withno dire results.If it can take the heat of molten metal, the lower temp. of sintering metalshould not be an issue.-----== Posted via Deja News, The Leader in Internet Discussion ==----- Create Your Own Free Member ForumLets be sure we're talking about the right stone here. Are you referring to thetrue synthetic Alexandrite, which duplicates the natural chrysoberyl chemistry?Or are we talking about the much cheaper synthetic flame fusion sapphire thathas a color change and is so often used as, and incorrectly called, syntheticalexandrite? The flame fusion corundum is the one I've seen people cast inplace. I'd personally be very leery of trying this with the true syntheticalexandrite, which isn't so cheap, among other things.
ALEXANDRITE : By the way, for the record, the synthetic sapphire product (or any sapphire,natural or synthetic) if exposed to these temps, should be kept in a neutral tooxidizing atmosphere, and not covered with fluxes. It's an oxide, after all.high temp reducing atmospheres can damage the surface polish by starting toreduce the aluminum oxide to aluminum, which reverses instantly, of course, butin the process, messes up the stone. The same with fluxes, which dissolveoxides, including aluminum oxide, etching the stones. Excellent point about the oxidation of the synthetic alexandrite-likesapphire's reaction to heat. I also found myself saying that the corundumcould take the heat without taking into consideration that oxide reaction ofthe AlO2.This is a good example of why it is good to get some extra view points on asubject before turning on the flame.
ALEXANDRITE : Well done, Peter. Thanks for providing some needed considerations that mayhave been overlooked by many others also.Be careful with this logic. It may not hold. first, be SURE you're talkingabout the same stones here. Actual synthetic color change chrysoberyl(alexandrite) is not a stone I'd expect to survive reliably. Maybe it would,but I'd sure want to test that theory a few times before risking decent stones,as these are not so cheap. Sythetic "alexandrite-like" corundum, on the otherhand, which is the very common flame fusion color change synthetic sapphire sooften marketed as synthetic alexandrite, might make it OK, and is cheap enoughto experiment with.As to the logic: When you cast stones in place, the stones are held in aninvestment block, which greatly reduces the speed of temperature changes andtemperature shock, and molten metal hits only a few small areas, and the coolsquickly to the investment temp. In short, though there is molten metal contact,the stone is not actually held at those temps at all, and the really hot contactis quite brief. In sintering PMC, the sintering temperature involved is onlyslightly below the actual melting point of fine silver. Since fine silver meltshigher than, say, sterling silver, or for that matter, many gold alloys, thismay actually be higher than the casting temps of some metals you'd cast in placewith, and more, the sintering operation is a sustained one, and the stone wouldhave to withstand these high temperatures for the entire sintering time. Also,Without the slow ramp up to sintering temperature that a normal burnout cycleprovides, the stones in fireing PMC may be subject to higher rates oftemperature change, and this change (shock) is potentially the most damagingaspect of either casting in place or sintering stones in PMC. You can reducethat shock with PMC by firing the stuff by placing it in a closed, cold kiln,and bring it to fireing temp without opening the kiln, waiting the required timewithout looking at it (opening the kiln could send a current of cold air in atthe stone, potentially breaking it), and when the times up, just turning thekiln off to cool slowly. And finally, it's significant to recognize that theatmospheric conditions surround the stones will be different, especially at hightemp, between casting in place vs. firing PMC. Reducing atmospheres or fluxesin particular, might cause significant surface damage to these stones. Inshort, just because you may be able to cast a stone in place is no guaranteethat it will withstand PMC. The two processes are sufficiently different as torequire seperate testing. And this is the key to this question. Use a littlebit of PMC, along with an expendable sample of the stone: Perhaps a smallmellee, or a cracked one or something. Test the process and see.
ALEXANDRITE : Hello there, I have been given a piece of heirloom jewelry by my mother. It is aring of hers that was purchased secondhand in the mid 1950's. It is avery unusual stone, in both cut and color. The cut is a fancy,diamond-shaped cut with a twisting of the top and bottom points of thediamond shape, giving the stone a "swirl" look. The color is a deep violet in artificial light, and it changes to a verydeep, rich aqua/teal color in sunlight. She was told that it was"Alexandrite". I was under the impression that all Alexandrites, be theynatural or synthetic, changed from a deep raspberry red, to a brilliantgreen with differing light. The stone is set in a 14k white gold setting with a small diamond oneither side of the colored gemstone. It has no markings inside the band,except for the "14k" stamp. Does anybody know if synthetic gemstones are made, that change fromviolet to aqua? Is there a natural gemstone that displays theseproperties? Any info. would be greatly appreciated, as this is one of mymost favorite pieces. Thanks,
ALEXANDRITE : Yes, there are synthetic Alexandrites. My girlfriend has a beautiful one. It is my understanding, from her, that there are a variety of color variations to the artificial ones -- meaning they will change into many colors, though most stay to the blueish red variety.Hers was set in 18K gold setting ring so the setting has no bearing to the stone.Sandra********************************** *************************************** MOVEMENT AND POSTURAL DYNAMICS FOR DANCERS AND ATHLETES Including: Alexander Technique, Applied Physics, Biomechanics, Ideokinesis, Kinesiology, and more. Ballroom, Latin, Theatre Arts --- Artistic Skating -- Equestrians Contact: SANDRA LEE WOLLIN - EMERSON, NEW JERSEY 07630 U.S.A Ph: 01-201-262-1274 E-Mail: **************************************** *********************************As excepted from the Rec.Crafts.Jewelry Frequently Asked Questions...Alexandrite is a form of chrysoberyl that has the uniqueproperty of being a dark moss green in candescent lightingand bright candy red in flourescent lighting. It is a rarestone that commands a high price among chrysoberyls.Alexandrite is a stone that has a lot of misinformationsurrounding it; thus the reason for this particular FAQquestion.
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