Post subject: Gem Treatment Recipes: in Memory of Mark Liccini
Posted: Sun Oct 24, 2010 7:17 pm
Joined: Sun Oct 16, 2005 12:22 pm Posts: 15801 Location: San Francisco
I think it would be interesting to compile a list of treatment recipes. I was inspired to start the list when I stumbled on a stockpiled pdf when I was searching for something unrelated and it reminded me of a thread we started in 2007: http://web.archive.org/web/200102211008 ... /Notes.htm
I've done a little research on the person who compiled this original list, Mark Liccini, only to discover, it appears as though he passed away in 2002. I've taken the liberty of reformatting and rewriting some of this info and adding additional information which has already been posted on the forum. Please also feel free to add any information you have on what is appearing to be a legendary lapidary icon: Mark Liccini.
We could add to the list, modify the list or remove things from our list. Eventually, we could add it, for permanent reference, to the Gemology Project. I'll start:
Beryl *Tip:For minimal breakage all heat treatment should be done on finished goods, which are as clean as possible. Slight fractures can spread,and included crystals can halo or burst. All heat treatments are best done by slowly graduating temperatures both up an down. All stones should be placed moisture free in a crucible and covered with a heat sink material such as beach sand,or better, powdered alumina.1
Aquamarine* Heating to 450C for one hour changes the valence state of the iron.
Aquamarine often has a residual greenish tone until it's heated. Why? G & G, Summer 1981, my hero George Rossman, wrote an article entitled "Color in Gems, The New Technologies"
To paraphrase. Beryl is a berylium aluminum silicate. Yet, none of those elemental constituents are able to cause color. Iron is responsible for golden yellow, golden green, green and blue beryl. In order to understand how minor amounts of iron impart various colors we need to know: 1. where within the atomic structure of the beryl the iron is located 2. the oxidization state of the iron.
The blue and yellow color seen in beryl results from small amounts of iron situated in the channels formed by silicate ions, running parallel to the "c" axis of the xl. If the iron present is in the 2+ oxidation state, the color is blue. If it is in the 3+ oxidation state the color is golden yellow. Combinations of oxidation states impart intermediate colors.
When you heat greenish blue beryl to 450 degrees C, it reduces the iron from 3+ to 2+, therefore eliminating the yellowish cast. All Aquamarines with a greenish or gray cast, heat to purer blue, some darken Dichroic Greens/Blues become uniform Blue
Green Beryl*: Does not alter as the result on heat treatment1
*Tip: To help determine if a greenish beryl can be altered with heat, one can use a polaroid filter. Hold the stone under direct incandescent light,and rotate the filter in a circle.If a color change is apparent, the color CAN be changed. If no color change is seen, the material will remain unchanged if heat treated.1
Orange Morganite⇒ Pink left in direct sunlight for 1-2 weeks or heated at low temperature 205C 1
Peach Morganite⇒ Green After heating to colorless at 450C, the beryl is irradiated with Cobalt60 at 450 mega-rads to produce assorted greens If, the green is subsequently heated to 180º C, it will be converted to pink.1
Colorless Beryl, Very Light Aquamarine/Morganite Irradiated with Cobalt60 at 450 mega-rads, usually turns to Straw Yellow, but this has also been known to produce red, purples and gray1 At levels of 3,000-5,000 mega-rads, changes predominately to Dark Canary Yellow and "Precious Topaz like"Orange"1 Warning: If beryl has a high content of Cesium, irradiation with Linear Accelerator can become highly radioactive, taking 100s of years to "cool" down. 1
EMERALD: Clarity and color can be dramatically improved with oiling, oiling with color additives, filling with cedar oil (preferred), Canadian Balsam or filing with "Opticon".1 Oiling First, soak the stones in Acetone,"Attack":, etc. Heat the stones slightly (hot plate) and while still warm place in Oil or Balsam* overnight. *Tip: Better results can be achieved with Cedar Oil and Balsam, if the first step is done in a heated vacuum chamber. Then, transfer, under vacuum, to a hydraulic pressure canister and left for 24 hours.1
Opticon: follow manufacturers instructions. Opticon yellows with age and is not an acceptable treatment within the trade.
Amethyst: Lighten tone I believe only amethyst from certain locals will lighten when heated. Most will alter to citrine.1
Amethyst (Local: Pal D'Arco) Dark goods lighten at 390C for 1 hour.more hours; longer heating time does not increase lightening Will not alter to citrine1
Amethyst (Local: Jacobina) Dark goods lighten at 390C for 1 hour. Will not alter to citrine1
Amethyst (Local: Bolivia) :Lightens only from 390C and up.1
Amethyst (Local: Brezeina): Heated at 450C for 1 hour overall "cloudy look": All unzoned material heats to medium/light Citrine Brown zoned material treats to dark Citrine1
Amethyst (Local:Maramba): Heated to 450C for 1 hour All material treats to medium/light Citrine Brown zoned material turns to dark Orange1
Amethyst (Local:Rio Grande do Sul) Heated to 450C for 1 hour All material treats from light to dark Red/Orange; No brown zoning1
Amethyst (Local:Uraguay) Heated to 450C for 1 hour All material heats to a light to medium Lemon color 1
Amethyst (Local:Rhondonia and Goais) Heated at 450-500C Material turns to a Brownish Maderia Color Heated 390C, for 1 hour Dark goods lighten1
Smoky Quartz Heated to 450C for 1 hour Stones with brownish zone heat to Lemon Yellow, just in that zone1
Colorless Quartz⇒ Smoky Quartz: Irradiates to Smokey color at .5-1 mega-rad, Cobalt 601
Additional Temperatures, needing more information:
Reddish Brown Zircon to Blue: 1000 degrees C in a reducing (oxygen free) environment2
Reddish Brown Zircon to Colorless 900 degrees C in air2
Orange Beryl to Morganite: 400 degrees C2
Yellow and Brownish yellow topaz to Pink: 550 degrees C2
Topaz (all colors) to Colorless:1000 degrees C2
Dark Green Namibian Tourmaline will brighten Significantly:370 degrees C2
Brownish Green Zoisite to Tanzanite:370 degrees C2
Sapphire containing titanium to develop or brighten color:1600 degrees C2
I have heated, over the years, with some success, tanzanite, aquamarine, amethyst, and recently tourmaline in my normal jewellery burnout kiln.
I also have heated many other stones with spectacularly bad results. Amongst others, larimar, (went white) lavulite (went brown) smoky quartz (trashed.) Aqua (white), citrine to try and make it lighter (crashed) .
Just a few weeks ago I took some dark olive green tourmaline and in a fit of lethargy put some in the oven.. I think it is Zimbabwean material and it had already been very badly cut. (faceted) It was lousy stuff, completely un- sellable . The material is clean though. Clean materialis is the best to experiment with.. Although, I have put stuff in the oven that had fractures and did not get more badly fractured.( even though the color was not necessarily better)
So this is how I got this tourmaline to a better color.
I took a stainless steel egg cup and filled it up with Satin cast 20 casting powder. Same stuff you cast jewellery with. Then I took a tourmaline and cleaned it with alcohol and pushed it to the middle of the egg-cup. Tapped it down firmly and put it into my oven.
300C I leave it at the temperature for about an hour ( it is only an egg cup so it saturates through quickly), then I take the egg cup out of the oven and let it cool outside until room temp. I don't care for this million hour cooling down bit, because I am only playing around, and the material sucks anyway, so I can afford to trash it. No change.
400C Same as above, no change
500C Some change, and it goes a little bit lighter. I use a control stone of the same original colour to check. Then I go up into 50C increments
At 550C was my best color, noticeably lighter. I went to 650 with this stone, and there was no more color change, so I called it quits. At least it will be sellable after have I recut it. With disclosure, of course. By the way, it did not lighten the c-axis at all, so essentially it still remained junk.
Then I took another one and did the same thing some days later. This time after doing the same as above,there was no change in colour at all. Even from a similar source, or parcel from the same mine, stones seem to react differently to heat. Anyway, that is my non-scientific experience.
So I decided to increase the temperature in hundred degrees segments until something DID happen. This is not something I would normally do , but I just wanted to see how high I could take a heat sensitive stone like tourmaline.
At 700C, nothing had happened to the dark olive green colour. And I was not even careful to cool it down slowly, other than putting the egg cup outside the oven. 750C Nothing. I certainly did not think a tourmaline would go so high.
At 800c it died. (At that temperature the oven is a bright orange inside) The tourmaline had became brown and now looks a bit like petrified wood. ( if I knew how to put a picture in this post, I would ) Ok, so that's extreme. I have never heated tourmaline to that temperature and I wanted to see how high it would go..
Most stones I have played with are in the 300 to 550 maximum. Some work, most do not. About ten years ago I heated tanzanite rough to 400-450C . Of the three stones, two went better and one died. I think I used building sand in a smelting crucible then. If I am serious, I will let the oven cool down to room temperature before I take the stone out. Sometimes, I just put a piece of stone into my casting cycle, just to see what happens. I take it out before I go too high, like over 550C. Mostly they trashed..... Hans Meevis
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