elementary
fully equipped rock polisher
Member since February 2006
Posts: 1,077
|
Post by elementary on Jan 29, 2012 23:48:55 GMT -5
Thunder69 sent me a box of his Mississippi agates a while back and I've had fun polishing a specimen or two every few months. The golden colors of these agates are wonderful, and the patterns in the agates is very detailed and ornate. While reading over June Zeitner's Southwest Mineral & Gem Trails Guide for the Southwest (Lapidary Journal (C) 1972) I found a paragraph that caught my attention. pg 137 First of all, Zeitner claimed that a skillful cutter could cut cat's eye stones from the rough. She didn't give details. But when it came to heat treating, there was quite a bit. Ken Kyte is said to have developed a heat treating method for enhancing the color to brighter oranges, yellows, reds, and pinks. He would pack the agates in large containers of sand, then put them in a gas oven (his was one he had rigged outside). He turned up the heat carefully, 50 degrees at a time, until it was as high as it could go. Then he left it on 'for a while' and then started to turn down the heat. Once the heat was off, he left the agates in the cooling oven overnight without peeking. The color is said to have gone completely through the stone - and doesn't look artificial - just an augmentation of what color the stone had previously. In the stones I have, I can see some that look red or pink or yellow or orange, and if the heating works, their banding is going to be outstanding. So - any advice on what containers might work best with this, what might have been the max temp of ovens in 1972, and is anyone willing to try before I destroy my own oven??? You can see samples of this agate on John's thread: forum.rocktumblinghobby.com/index.cgi?action=display&board=specphoto&thread=41668&page=1Thanks for any advice, Lowell
|
|
|
Post by Woodyrock on Jan 30, 2012 1:36:09 GMT -5
Lowell:
Knappers regularly cook agate to make it more knappable. Some guys used pottery kilns with special heating switches to slow down the heat increase to about 50 degrees per hour. The other way of cooking rock, and a popular one is to buy an old turkey roaster. the new ones only go to 600 degrees, but some old ones go the 700. Most agate needs 650 to 750.
Talk to your wife about the methods the ancients used to cook rock. Most agate, and flint need to be heat treated to make them knappable..........and since the cooking changes to colour, it is quite obvious which material has been heat treated.
Much Brazialian agate has been heat treated to enrich the colour.
BTW it is better to buy a turkey roaster than to use the wifes oven...most women object to the odour cooking rocks make. Woody Woody
|
|
Deleted
Deleted Member
Member since January 1970
Posts: 0
|
Post by Deleted on Jan 30, 2012 17:41:57 GMT -5
|
|
Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,466
|
Post by Sabre52 on Jan 30, 2012 20:01:51 GMT -5
I unfortunately, tried it in my wife's oven and heated the rock too fast. Agate blew up and sprayed sand all over the place. The agate, which was Brazilian slabs, did have a nice color change and I actually got a cab or two from the fragments of the slabs. Unfortunately I also got a good chewing out from my wife....Mel
|
|
elementary
fully equipped rock polisher
Member since February 2006
Posts: 1,077
|
Post by elementary on Jan 31, 2012 10:05:44 GMT -5
Damn, that's it!!!!
My school has a kiln!!!!!!
A hahahahahaha!
And nobody is using it right now!
Time to play Dr. Frankenstein!
Thanks for the heads up,
Lowell
Now to double check what kind of container could handle the heat and sand.
|
|
|
Post by NatureNut on Jan 31, 2012 10:51:29 GMT -5
Cast iron dutch oven?
|
|
Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,466
|
Post by Sabre52 on Jan 31, 2012 18:32:21 GMT -5
Lowell, be careful and get instructions before using that kiln. Folks kill themselves blowing those up all the time....Mel
|
|
carloscinco
fully equipped rock polisher
Member since July 2008
Posts: 1,639
|
Post by carloscinco on Jan 31, 2012 18:40:55 GMT -5
I would think one of those disposable aluminum baking pans would work. They make a deep gallon pan. Aluminum melts at 1200 F. Buy two and keep them nested to hold the heat during the cooldown.
|
|
elementary
fully equipped rock polisher
Member since February 2006
Posts: 1,077
|
Post by elementary on Jan 31, 2012 21:36:30 GMT -5
Mel - and everyone else,
I would never do anything that would put children at risk. My goal is to talk to the woman (artist) who was the advisor when we bought the kiln.
Nor am I going to misuse equipment bought with school money (or my own.) I'll be taking this whole endeavor slowly.
Thanks for the concern. I'm just excited to try this thing, but I won't be reckless in pursuing the goal.
But man - I am really curious about the results.
Lowell
|
|
|
Post by jakesrocks on Jan 31, 2012 22:23:45 GMT -5
I'd say to use a Pyrex casserole dish with lid, and do small batches. Pyrex will handle the heat, and with the lid on will allow for slow cooling. Don
|
|
|
Post by paulshiroma on Jan 31, 2012 23:06:38 GMT -5
And however, you do this, make sure to take before and after photos. I'm really curious now. Interesting thread, Lowell.
Paul
|
|
Sabre52
Cave Dweller
Me and my gal, Rosie
Member since August 2005
Posts: 20,466
|
Post by Sabre52 on Jan 31, 2012 23:23:18 GMT -5
Yup, I'm dying to see pics too. If it's cool, I'm going to try and find one of them old cookers myself and try it again because I'd like to heat treat flint for knapping. I stumbled across an old Indian camp the other day where they had obviously heat treated some of the local flint and it was way more colorful than the untreated stuff. Would make a very pretty tumble. Wouldn't have mentioned the kiln thing Lowell except someone I knew once took a ceramics class one time and the teacher had some horror stories about exploding kilns. Probably gas ones or something and maybe she was just trying to scare the students who paid her for her kiln services but I don't know..Mel
|
|
snuffy
Cave Dweller
Member since May 2009
Posts: 4,319
|
Post by snuffy on Feb 1, 2012 5:46:15 GMT -5
I was wondering about using an outdoor gas grill.Mine has 4 burners,could turn on 1 burner ever so often to increase temperature.Gauge goes to 1000.I have in the past accidently gotten it over 600.Propane may make it cost prohibitive though How many hours would be involved?.Anybody ever try this? Maybe cover the top of the grill with an insulated product to hold heat better?
snuffy
|
|
mjflinty
spending too much on rocks
Member since September 2011
Posts: 358
|
Post by mjflinty on Feb 1, 2012 10:20:02 GMT -5
I'm a knapper and a lapidary and have heated lots of rock for both purposes. In the knapping world, we have rock recipes (think cookbook) that have been tested and used for years by other flintknappers. I took a look at the agates that you want to heat treat; I don't think I've ever seen a recipe for it. That means you'll have to experiment more. Here is the best fit I can think for your stone. First, you don't want to try to heat the pieces if they are thicker than 2 inches. Slabs heat treat better and in a more regular way than odd shaped thick nodules; think about how a turkey needs longer to cook because the heat has to get in to the center... same thing with rock. Now, you don't have to use a sand bath but, I would recommend it because if they blow, the sand will stop any potlids (shrapnel) from escaping into the kiln. Use any pan that you can put in the oven. You'll start them at 250 and hold them there for an hour and then raise the temperature 50 degrees each hour until you hit 500. Then let them soak at 500 for about 4-5 hours. Turn the kiln off and let it cool on its own; if the stones are exposed to cool air they will craze and crack and be worthless. When you take them out of the bath (should be cool to the touch) you should see the red colors you are after, if not you'll have to repeat the whole process and go to 550. I know that 50 degrees doesn't seem like much but, you can lose a whole batch of rock due to 25 degrees. If you do see the reds, they may only be skin deep... so you'll have to test one and make sure the heat penetrated deep enough in to the stone. If you have any questions feel free to PM me.
Good luck! Michael
|
|
elementary
fully equipped rock polisher
Member since February 2006
Posts: 1,077
|
Post by elementary on Feb 1, 2012 20:54:15 GMT -5
A huge thank you Michael for that info!
Don, I was wondering if pyrex would work as well.
I'll keep all updated with the adventures of toasting agate.
Lowell
|
|
|
Post by jakesrocks on Feb 2, 2012 10:38:01 GMT -5
Hey Lowell, one thing that wasn't touched on here is water content in your agates. If they wave lots of small cracks, they may contain water. You might want to dry them out in the oven for an hour or so before trying to heat treat them. Water and heat = steam, which could cause a rock explosion in the kiln. Over the years I've had a few camp fire ring rocks explode when exposed to the heat of the camp fire. Don
|
|