Potters & Sculptors - Making Rock from Mud
I have not found a ^6 Flameware Clay Recipe so I'm trying to adjust ^9 flameware recipes. Ron Propst's flameware clay body recipe (below) has a thermal expansion of 5.25
My initial thoughts are:
1.) replace the 10% Custer Feldspar with 10% Talc, resulting in an expansion of 4.82 according to Insight.
2.) add 5%? Lithium Carbonate or Lithium Fluoride with a thermal expansion of 5.28 - closer to the original. Or does this increase Lithium enough to present a leeching problem?
3.) would I end up with a stronger fired body if I replace some or all of the AP Green Fire Clay with Kyanite? With Kyanite the expansion is 4.88 for option 1, and 5.33 for option 2, but those Kyanite needles should make the ware stronger.
4.) I've also noticed that the original flameware clay body is very spongey like a marshmallow, yet not very plastic. Is this just typical of a body with a high percentage of spodumene? I used 3% VeeGum Bentonite rather than 2% Bentonite and 1% Macaloid, but I'd be surprised if that made a large difference.
5.) Of course the ^6 glaze recipe will have to have a thermal expansion just a little higher than the clay, but I'm more comfortable with glaze chemistry.
Flameware Clay Body - Ron Propst
Low 5.25 Thermal-Expansion clay body for stove-top cooking pots
Spodumene 30.000 29.13%
APG Fireclay 30.000 29.13%
Ball Clay 20.000 19.42%
Pyrophyllite 10.000 9.71%
Custer Feldspar 10.000 9.71%
Bentonite 2.000 1.94%
Macaloid 1.000 0.97%
Calculated Expansion 5.25
Robbie Lobel Flameware Casserole Dish
I just received some bisqued samples of my batch of Ron Propst's ^9 flameware.
It's very lightweight and porous, like the firebrick used in electric kilns, but far more durable. It's very difficult to break one of these bisqued tiles.
I wonder if some Darvan might deflocculate the clay body and make it denser and not so spongey. Bentonites add plasticity to clay bodies, but maybe 3% VeeGum left the clay too flocculated.
Is this tile Ron Propst's ^9 flameware or your modification? Did you replace the AP Green with Kyanite?
I have made many cooking pots with very porous low fire earthenware, and they are very wonderful to cook in but not the most durable. They are cheap to make and cheap to fire however.
Right now I am developing a castable to use in a bread oven kit. What I need is something that has very low dry & fired shrinkage & can take the heat shock, plus hold as much heat as possible. I'm getting close with a talc body fired to ^ 1.
Harold - The post you're replying to was the start of a long process. Ron Roy referred me to George Tsitsas of Marrowstone Pottery.
They have this PDF file (link below) on their website called "A Discussion of Flameware".
In order to survive rapid cooling and expansion, the ceramic body has to have a very low COE (expansion rate) which requires a suitable Cone 6 flux lithium, or similar low-expansion flux. As a result, normal glazes will just shiver off the body, so you have to develop lithium glazes which are similar to the clay body. If you like clay chemistry, you'll have a lot of fun developing your clay body and glazes.
The three or four potters best known for "flameware" have each created their own unique solution to this problem, and more or less jealously guard their "trade secrets".
I've promised George Tsitsas I won't pass on a lot of the knowledge he has gained through long experience. But I can tell you he is adamant that the key to developing your own low-expansion clay body is the use of a dilatometer to measure the COE of your clay samples, as small changes can create a large change in COE. I think Ron Roy still tests fired clay bars in his dilatometer for a fee, and there are a number of labs which do so as well.
An Orton Dilatometer (used to measure the expansion of a bar of fired ceramic as it is heated)
If there is one primary secret, it is creating a flameware body which has plasticity without excess flocculation which causes the body to have an undesirable marshmallow texture, which I displayed in the posts above last year. Since the plasticity typically needs to be provided by Macloid or similar charged clays, one important key is the use Distilled or Reverse Osmosis water to mix the ingredients. The less fewer free calcium and magnesium ions you have in the water, the better the chance that your flameware body will have a clay-like texture which can be thrown or formed in a traditional manner.
The PDF file puts you on the right track.
George Tsitsas testing a glazed bowl. http://www.youtube.com/watch?v=WFwZ1x6JoVs