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Post by deb193redux on Aug 28, 2013 22:27:17 GMT -5
yellow to red makes sense. likely the color is from iron hydorxide
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Post by helens on Aug 28, 2013 22:29:03 GMT -5
White,grey and black rarely change. Makes sense. Very likely there is little iron. Typically yellow turns orange. Orange turns red or brownish red. Red often turns brown or darker red. But other colors from who knows what happens in the coral. Often the color-coral. Go figure. And lavender or purple. I thought I said that? LOL!
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jamesp
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Post by jamesp on Aug 28, 2013 22:36:44 GMT -5
Well, the corals that turned red in heating all started out yellowish, so when the stone is starting out greyish, it may not have enough whatever chemical to go red. I wasn't thinking about that... but makes sense:). I felt moved to elaborate too. I did include a bit extra. I forgot to add transparent changes to cloudy. I looked at a welding rod cooking oven-used at the industrial junkyard. Thermostatically up to 550F. I would put a higher watt heater. Holds about 3 cubic feet. Need 650F
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Post by helens on Aug 28, 2013 23:27:42 GMT -5
Why not just buy a used kiln:P?
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jamesp
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Post by jamesp on Aug 29, 2013 6:49:56 GMT -5
I will never go over 650 so these weld stick ovens are beat up and tough. And $50... And 8 miles away. And light weight. But ya never know. I will try it. And it is cheap and easy. But i have failed tinkering with stuff like this but not too often. Sometimes my neck gets tired of supporting oversized brain(wife says butt head). many times doing cheap experiments like this. but that oven probably cost 8-900$ new. Looks like this one Helen
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Deleted
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Post by Deleted on Aug 29, 2013 8:11:28 GMT -5
Those are really pretty!! I thought Morrocans were red tho? some berber agates are red. a lot are just gray & white banded. it is a whole country with a number of different types of agate. you would not say "I thought American agates were mossy" But you could say that all Montana agate is clear to coffee colored and sometimes it has some black in it. And there are a lot of other agates in Montana. Jim
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Post by deb193redux on Aug 29, 2013 8:56:37 GMT -5
you would need to be careful about a kiln, it can reach temperatures that would shatter the rock. You do not need much more than conventional ovens can deliver.
It is actually possible to make black agate, but then with too much heat, the carbon oxidizes and the rock goes back to clear. Have to do this with a rock that will not shatter. I have heard about overcooking adamooka opal and the matrix goes form black to back to original color. I think diamonds burn at about 1500 degrees. Any got a 10 carat they want to test in a kiln?
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Post by helens on Aug 29, 2013 9:17:22 GMT -5
I can't find it now, but I saw a crazy experiment this guy did with a diamond in a kiln... he put a faceted diamond that was defective somehow in a kiln to see what would happen, and I THINK (forgot exact temp) that the diamond began to deform at around 1100 degrees. We don't need to test it again O.o.
Anyway, you MUST have a kiln with a pyrometer to regulate the temps precisely... not just a kiln you shut off. A kiln can be set to hold at 200 degrees if you want, just because it CAN go to 2500 degrees (mine does, most don't go that high) doesn't mean you have to bring it that high, you can get very precise on kiln temperature controls if you have a digital pyrometer.
I have definitely discovered that what Daniel just said was true with the coloring first then going back to the original color. Also, the cracking problem. I tried to put a few pieces of rocks in with my glass while annealing, and wow... what a mess when they exploded! LOL!
But when cooking corals, I'm thinking the holding time is also very very important. Ie, holding the temp with very gradual temp reductions to give the rock a chance to even out temps, and possibly anneal too.
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jamesp
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Post by jamesp on Aug 29, 2013 9:56:45 GMT -5
Daniel is right Helen. Most kilns can get hotter than necessary and and are overkill.A heater that is sensitive in the range of 200-800F is perfect and cheaper . Your glass kiln is dead accurate.
It is just too nice and probably too small for my projects. I may preheat buckets of rock covered in sand to 400-500F on the wood stove for 16-24 hours and them pop em in the electric stove
to reduce costs. Big chunks need slow long ramp ups and ramp downs otherwise they will pop. if you are going to saw them for cabs or break it down to tumble then it does not matter if
a 12 pound chunk cracks in 2 or 3 pieces. The stove above is 1600 watts which is small enough for 20amp 110VAC wall circuit. I will convert to 220 and go to 2000 watts and plug it to the welder
circuit.
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jamesp
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Post by jamesp on Aug 29, 2013 10:06:20 GMT -5
Notice the temp for coral is 450 - 600F. Glassy coral at 450-500F. Grainy coral at 600-650 F
Agate Brazilian - 450-500 Agate India - 500 Agate Mexican - 500 Agate Montana - 550 Agate Moss - 450 Alibates - 425-500 Bloodstone - 500 Burlington - 600-650 Coral - 450-600 Dacite - NONE Flint Ridge - 500-600 (set the roaster at 200 degrees for two hrs then increase until the max temp. is reached and leave it for 12 to 24 hours) Flint - Fort Hood - 400-550 Flint - Georgetown (Blue and Black) - NONE Flint - Georgetown Banded - NONE to 400 Flint - Knife River - 350 - 450 (Do NOT overheat or it could pot lid) Flint - Danish - 300 -350 Flint - British - 300 -350 (hold time could be 6 hours) Jasper Red - 500 (very hard stuff to work) Jasper Sunset 450-475 Jasper Fancy 450-500 Jasper Picture 525 Kay County - 500-600 Novaculate - 700-900 Obsidian - NONE Pedernales - 450 Petrified Wood - 300-450
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jamesp
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Post by jamesp on Aug 29, 2013 10:09:56 GMT -5
This is about right. I hold thin pieces for 3-4 hours and thick pieces 8 hours.
" The same goes for the oven, but after the wife banned me, I got a turkey roaster and love it and would not go back. It is larger so I can put more in, spread them out differently, leave the sand in it and not worry about burning out the internal mechanisms. The 18 quart ones have temperature gauges that goes up to 450, or 550 on the more difficult ones to find. You can get the temperature up an additional 100 - 150 degrees more by removing the middle pan. They can go anywhere from $40 to $300. The one pictured above was purchased brand-new for about $45; A significant savings from a kiln!
It is simple to use. Spread the slabs (preforms) out, slabs on their side, and pour sand over then making sure they do not touch one another. Note that hotter temperatures will be generated at the very bottom of the sand (reverse from the fire method) and the sides.
I found that the best method was to:
Heat roaster (with sand and rocks) for two hours at 100 degrees Bring it up 50 degrees every hour Once it reaches the desired temperature leave for an hour and reverses the process; Or, Once it reaches the desired temperature leave it there for a couple of hours and turn it off. The above last two points really depends on the stone. Sometimes when it reaches the desired temp, it is heated perfectly. Other times, it needs to be maintained at that heat for a certain period of time. If you surpass it on some stones, they turn to dust.
Since I do not get a lot of material, I usually try and throw pieces that require 450-550 degrees together and hope for the best. I have only lost one piece of jasper and a couple small slabs of wood using this approach.
Note: Some people do not even use the sand with mixed results. They just throw the stone in and get to it. Basically the sand does two things. One it maintains the heat evenly, allowing the temperature to slowly raise and cool. And two it keeps the stone from touching one another. Both achieve the same goal by preventing surprises to the stone that might cause it to explode or crack. Since I buy rock, I will not take any chances of breakage and will stick to the sand.
When I first tried heat treatment I wanted quick and dirty rules, "how much-how long". But I quickly learnt that different rocks need different temps and hold times. To make it worse, the same stone is NEVER the same and batches of the same rock, i.e. Brazilian Agate, may lead to different results for each slab."
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Post by helens on Aug 29, 2013 11:34:41 GMT -5
James... what are you doing with those VAST quantities of cooked corals that you need drum tumblers and drum heaters??
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Fossilman
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Post by Fossilman on Aug 29, 2013 11:43:32 GMT -5
Cook them and find out! James has a recipe...........
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Post by helens on Aug 29, 2013 11:44:47 GMT -5
I have. Very pretty. But I don't need DRUMS of it:).
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jamesp
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Post by jamesp on Aug 29, 2013 15:08:57 GMT -5
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Post by sheltie on Aug 29, 2013 15:14:41 GMT -5
Notice the temp for coral is 450 - 600F. Glassy coral at 450-500F. Grainy coral at 600-650 F Agate Brazilian - 450-500 Agate India - 500 Agate Mexican - 500 Agate Montana - 550 Agate Moss - 450 Alibates - 425-500 Bloodstone - 500 Burlington - 600-650 Coral - 450-600 Dacite - NONE Flint Ridge - 500-600 (set the roaster at 200 degrees for two hrs then increase until the max temp. is reached and leave it for 12 to 24 hours) Flint - Fort Hood - 400-550 Flint - Georgetown (Blue and Black) - NONE Flint - Georgetown Banded - NONE to 400 Flint - Knife River - 350 - 450 (Do NOT overheat or it could pot lid) Flint - Danish - 300 -350 Flint - British - 300 -350 (hold time could be 6 hours) Jasper Red - 500 (very hard stuff to work) Jasper Sunset 450-475 Jasper Fancy 450-500 Jasper Picture 525 Kay County - 500-600 Novaculate - 700-900 Obsidian - NONE Pedernales - 450 Petrified Wood - 300-450 Y'all have me so confused I don't know if I'm coming or going! All I want to know is can you put these in a kitchen oven? Is so, at what temp and for how long?
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jamesp
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Post by jamesp on Aug 29, 2013 19:34:21 GMT -5
I will guess the temp for that material at 500 degrees F. I do not know what the treatment temp is for Morrocan Agate. And could not find it. So i posted the list so you can see what is typical.
If your oven goes that high then you can cook it.
Pack it in sand and heat it 100-150-200-250-300-350-400-450-500 changing temp each hour. Hold at 500 for 2-3 hours and turn the oven off and leave it closed to allow rock/sand mix to cool slowly. Probably about 10 hours later you can remove the rocks from the sand.
I hope your oven is in good shape. It is a long time to run an oven.
That's as simple as i can tell you. And that should be fine for rocks under 1/2 pound.
It is expensive process. I cook 40 pounds at a time(plus 15 pounds of sand).
Good luck.
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Post by helens on Aug 29, 2013 21:45:45 GMT -5
Denny, JamesP posted a bunch of threads about cooking agates a few months back.
I tested as high as 750 degrees, which actually gave me the best colors, but made the pieces crack apart (in my case, I didn't mind, since they were too big to begin with). You aren't going to get 750 degrees out of an oven tho.
You have nothing to lose to try it in a regular oven at 500 degrees, but as James said, it is a long time to run an oven for. If you don't mind, it's worth trying!!
Also, the sand pack James mentioned is probably a great idea to help keep the temp even to prevent cracking. I did them dry directly in the kiln, but my kiln has great temperature control to the individual degree, and I took the temp up very slowly. I kept all the rocks in there for about 24 hours each time.
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