ejs
spending too much on rocks
Member since July 2008
Posts: 478
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Post by ejs on Apr 14, 2009 21:46:07 GMT -5
After completing a lengthy tumble of some carnelian agate, I was happy with the shine but displeased with the final color. See: forum.rocktumblinghobby.com/index.cgi?board=trtphoto&action=display&thread=29737Here is how the batch looked when it was done its tumble (before cooking): image1:  Following suggestions made in that thread, I decided to try cooking the carnelian to see if it brought out a different color. I placed the Carnelian within sand (white play sand) in a oval turkey roasting pan: image2:  image3:  And then placed it in the oven: image4:  I cooked it at 200 for 1 hour, 300 for 1 hour, 400 for 1 hour, and finished it off at 500 for 4 hours (my oven does not go to 550). I then let it gradually cool in the oven overnight. As you can see, it didn't make much of a difference: image5:  image6:  A few of the rocks did pick up some color, often along the edges or near a crack: image7:  image8:  Someone suggested that amethyst might turn golden yellow in this process, so I tried one piece of that. On the left is one of the original pieces, on the right is one that was cooked. There seems to be a slight change in color (or is that only because it is wet?) but nothing to write home about:  All in all, I'm a bit disappointed with the results. It did improve the rocks, but only slightly. I was hoping for a real amber color in the end. I can imagine two possibilities: 1. I need to run the oven up to 550. Maybe 500 just wasn't hot enough. 2. The material I started with just will not achieve the color I am seeking. I may try again with a toaster oven that goes up to 550, just for the sake of completeness. In any case, thanks for the advice, and thanks for looking! |
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Post by Tweetiepy on Apr 14, 2009 21:49:15 GMT -5
Try gold tiger eye next time - I'm sure the results will be much better
Nice batch even though! Pretty stuff - the purple is nice as always
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NorthShore-Rocks
fully equipped rock polisher
Member since December 2008
Posts: 1,004
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Post by NorthShore-Rocks on Apr 14, 2009 21:51:51 GMT -5
Nice experiment EJS! Thanks for documenting the whole process.
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MikeS
fully equipped rock polisher
Member since January 2009
Posts: 1,081
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Post by MikeS on Apr 14, 2009 21:53:13 GMT -5
Amythest will turn green with heat (that's how they make the "green amythest you see at jewelry stores), but it believe it requires a temperature above 450 degF for a pretty long period of time to do that....
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Post by bobby1 on Apr 14, 2009 23:25:01 GMT -5
Generally if the rough material has a reddish outer skin it indicates that at sometime in its development or history the Agate was exposed to iron compounds. Depending on how long they were exposed to the iron it will determine if it penetrated through the Agate. Because you got some color change there is a likelyhood that they will change color with more time at the higher temperature, posibly up to 500 degrees. There is also the possibility that the Agate will turn more to the brown shades. The process is somewhat unpredictable but the material is not particularly expensive, so go for it. Here is an example of some Brazilian Agate that I heat treated at increasing temperatures and times. The final one was at 500 degrees for 4 hours. Bob  Bob |
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Post by Michael John on Apr 15, 2009 2:59:51 GMT -5
A very common con in Brazil is heating amethyst. I don't know the temp or the duration, but it DOES come-out looking like citrine ... and they sell it as citrine (higher price).
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coasthunterjay
starting to spend too much on rocks
Carefull ive got a gun....and a closet full of rocks
Member since May 2009
Posts: 155
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Post by coasthunterjay on Jun 11, 2009 16:27:59 GMT -5
Hey might even try it in just a smaller container and try putting it in a gas grill...i know some of those get pretty freaking hot....and gas is alot better heat than using a cooking unit.
COOK IT FOR 4 HOURS AT THE HIGHEST TEMPERATURE might get the color change your looking for..........shoot try 6-8 hours as long as your cool with waiting on them.
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coasthunterjay
starting to spend too much on rocks
Carefull ive got a gun....and a closet full of rocks
Member since May 2009
Posts: 155
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Post by coasthunterjay on Jun 12, 2009 1:49:16 GMT -5
I JUST FOUND THIS FOR THOSE THAT ARE INTERESTED. MIGHT WANT TO POST IT IN ITS OWN POST BUT HERE YOU GO.... GREAT INFO....! SOME ONE MENTIONED ADDING A HEAVY RUSTED PIECE OF METAL TO THE TIN AND THE ROCKS MIGHT ABSORB SOME OF THE RUST AND TURN A RED-ORANGISH HUE. WHO KNOWS BUT VERY COOL! www.geocities.com/knappersanonymous/heat.html |
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Post by 150FromFundy on Jun 12, 2009 11:28:38 GMT -5
In nature, Citrine is burt Amethyst, but the temperatures to get that colour change are likely much higher than 500 degrees. In nature, rock can be heated to the jelly point, or even the liquid point.
Most "cheap" Citrine is burnt Amethyst from Brazil. The last batch of of Brazilian Citrine I bought still had flecks and inclusions of purple Amethyst in it. I beleive this process is done in a kiln (used for glass works and pottery) , not a conventional kitchen oven.
I think you will need higher temperatures to cook your Amethyst.
150fromFundy
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coasthunterjay
starting to spend too much on rocks
Carefull ive got a gun....and a closet full of rocks
Member since May 2009
Posts: 155
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Post by coasthunterjay on Jun 12, 2009 12:09:15 GMT -5
does anyone know what i mean by the cleaning stage on a kitchen oven....?
i bet the temperature a oven reaches and how slowely it reaches that temperature might be sufficient enough as long as you cook the rocks prior to it for a few hours at 200 degrees to make sure all the moisture is out of them......
ANYONE KNOW THE TEMPERATURE THE CLEANING STAGE IS ON AN OVEN? PRETTY LONG STAGE AND LET IT DO ITS THING AND SIT OVER NIGHT....PRESTO!
MIGHT BE AN IDEA FOR THOSE WANTING TO REACH HIGHER TEMPS......
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coasthunterjay
starting to spend too much on rocks
Carefull ive got a gun....and a closet full of rocks
Member since May 2009
Posts: 155
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Post by coasthunterjay on Jun 12, 2009 12:24:37 GMT -5
Ok i found some info on that.....the cleaning temperature in your oven is calibrated anywhere between 700 and 1000 degrees, typically around 800degrees.
Might be a little to hot....and i also read the maximum effective cooking temperature in most ovens is about 550degrees....regardless of style or type used.
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Post by MyNewHobby on Jun 13, 2009 13:47:38 GMT -5
Even though you did not get the signature color in your carnelian, I think it came out very nice, very pretty!
As always
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Post by Michael John on Jun 13, 2009 15:03:14 GMT -5
In nature, Citrine is burt Amethyst, but the temperatures to get that colour change are likely much higher than 500 degrees. In nature, rock can be heated to the jelly point, or even the liquid point. Most cheap Citrine is burnt Amethyst from Brazil. The last batch of of Brazilian Citrine I bought still had flecks and inclusions of purple Amethyst in it. I beleive this process is done in a kiln (used for glass works and pottery) , not a conventional kitchen oven. I think you will need higher temperatures to cook your Amethyst You're spot-on. In Brazil, they have massive kilns specifically for that purpose. It turns amethyst that golden color, but the unmistakable difference is that the finished product doesn't have the incredible flash of true citrine, and that's the dead giveaway. Almost every citrine cathedral sold is a heated amethyst cathedral. |
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