jgourlay
02-01-2007, 08:22 PM
Greetings all, and happy new year!
I am a total newbie to this and I've come to it as a good way to spend time with my 6 year old doing something other than television.
Thus far I've made 3 pots, with 1 firing successfully, and the other exploding owing probably to excess moisture. To fire, I'm using a bbq grill with internal dimensions of 12" deep x 23" wide and 6" tall. To date, I've used a mixture of mostly grilling charcoal with some coke thrown in. I can hook up propane, but not at a satisfactory rate of flow, although it does make a good adjunct to the charcoal.
The clay is a "Raku C" with "kaynite". The glazes I've used so far are: Envision foodsafe (Blue, yellow, and clear) as well as a supersaturated solution of salt (NaCl).
I am having a problem, and would appreciate your suggestions. What I am trying to achieve are (primarily) a "foodgrade" finish and (secondarily) pretty colors.
What I have found so far is as follows:
1. If I do ONE firing the blue comes out okay, the yellow and clear come out grey, and all three look like the cratered moon. The salt comes out a nice mild red, but does not seal the porosity and hold water (no surprise).
2. if I do TWO firings (first without glaze, second with), the cratering disappears, but the glazes seem to disappear as well except the blue. The doesn't glaze, but appears to soak in. I didn't try water in that one, but the surface texture looks like the non-water holding salt from above. The yellow and clear are just awol. The blue is there, but turns a kind of dull grey with some bluish tinge.
Note that so far I am firing the pots in the middle of a big heaping pile of fuel, with both the coke and charcoal piled directly on top of the work. I lay down a layer of fuel maybe 2" deep, then the work, then pile up charcoal into a cone shaped pile until it just begins to spile over the edge.
Here is what I believe I can control at this point:
1. Heat: more charcoal or less and charcoal closer or farther from the work. This is going to be a pretty coarse adjustment.
2. Heat and Airflow: lid up, or lid down. Lid down, less heat, less air, longer heating period. Lid up, lots more heat, much faster ramp, airswirls causing much less thermal uniformity, faster burn (less time in fire). I can, of course, keep dumping on charcoal but pretty quickly ash plugs up the holes on teh bottom at which point only the top surface of fuel has the high heat.
3. Number of firings.
4. Thickness of glaze painted on.
5. Choice of glaze (suggestions?)
I know I am reaching vitrification temperature as the pottery doesn't melt in boiling water--the water just soaks in. Also, as a reference, pennies placed in the pot will burn away leaving no zinc core and very little of the copper shell.
Any suggestions?
I am a total newbie to this and I've come to it as a good way to spend time with my 6 year old doing something other than television.
Thus far I've made 3 pots, with 1 firing successfully, and the other exploding owing probably to excess moisture. To fire, I'm using a bbq grill with internal dimensions of 12" deep x 23" wide and 6" tall. To date, I've used a mixture of mostly grilling charcoal with some coke thrown in. I can hook up propane, but not at a satisfactory rate of flow, although it does make a good adjunct to the charcoal.
The clay is a "Raku C" with "kaynite". The glazes I've used so far are: Envision foodsafe (Blue, yellow, and clear) as well as a supersaturated solution of salt (NaCl).
I am having a problem, and would appreciate your suggestions. What I am trying to achieve are (primarily) a "foodgrade" finish and (secondarily) pretty colors.
What I have found so far is as follows:
1. If I do ONE firing the blue comes out okay, the yellow and clear come out grey, and all three look like the cratered moon. The salt comes out a nice mild red, but does not seal the porosity and hold water (no surprise).
2. if I do TWO firings (first without glaze, second with), the cratering disappears, but the glazes seem to disappear as well except the blue. The doesn't glaze, but appears to soak in. I didn't try water in that one, but the surface texture looks like the non-water holding salt from above. The yellow and clear are just awol. The blue is there, but turns a kind of dull grey with some bluish tinge.
Note that so far I am firing the pots in the middle of a big heaping pile of fuel, with both the coke and charcoal piled directly on top of the work. I lay down a layer of fuel maybe 2" deep, then the work, then pile up charcoal into a cone shaped pile until it just begins to spile over the edge.
Here is what I believe I can control at this point:
1. Heat: more charcoal or less and charcoal closer or farther from the work. This is going to be a pretty coarse adjustment.
2. Heat and Airflow: lid up, or lid down. Lid down, less heat, less air, longer heating period. Lid up, lots more heat, much faster ramp, airswirls causing much less thermal uniformity, faster burn (less time in fire). I can, of course, keep dumping on charcoal but pretty quickly ash plugs up the holes on teh bottom at which point only the top surface of fuel has the high heat.
3. Number of firings.
4. Thickness of glaze painted on.
5. Choice of glaze (suggestions?)
I know I am reaching vitrification temperature as the pottery doesn't melt in boiling water--the water just soaks in. Also, as a reference, pennies placed in the pot will burn away leaving no zinc core and very little of the copper shell.
Any suggestions?