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hi guys i have some new ceramics mold up to 340 mm wide that i need to pre fire, but not sure about the firing rate and time . one program says a rate of 50c per hour to 800c ,,that's 16 hours ,,is this right ?? many thanks paul

need more info. are you firing green ceramics? if not i see no need to prefire. just kilnwash and use. r.

I've never pre-fired a mold BUT I just got a new one and the instructions say:

"pre-firing is recommended for molds larger than 30cm. this process strengthens the inner structures and makes the mold less susceptible to thermal shock." the directions are to go like you say below, 50 degrees C (122F) to 800 degrees C (1472F). no hold. let cool down at room temp. yes, that sounds like it would 16 hours to get to the temp but then it would take quite a few hours to cool back down to room temp.

What manufacturer recommends That? It makes no sense to me. R.

this mold is manufactured by Creative Ceramics and I think it was a Bullseye branded item.

huh. if the mold has been bisque fired. (those have) then it has been fired to above 1472. i can see no reason why doing like they said would do anything to the ceramic 'interior structures' or whatever. i just see no science behind that statement. cynthia m, you got a clue i am missing? r.

rosanna gusler wrote:huh. if the mold has been bisque fired. (those have) then it has been fired to above 1472. i can see no reason why doing like they said would do anything to the ceramic 'interior structures' or whatever. i just see no science behind that statement. cynthia m, you got a clue i am missing? r.

As a sometimes potter I agree with Rosanna. Firing an already bisqued mold to basically bisque temperature will do nothing to the internal structure. I have never prefired any of my Bullseye or other purchased molds.

mmmm seems i have opened Pandora's box ,,the moulds are from creative ceramics and 15 " round or across. the instructions say to pre fire at a rate of 50c per hour to 800c ,time 960 minutes ,,the trouble with this program is that my kiln controller will not handle that as it is just too slow,,,,,,so to pre fire or not to pre fire

Not. I never have and had a lot of those molds.

Makes you wonder what they are firing these slip cast molds to on their firing. There should be no need to fire it again. We bisque our thrown molds to 1900 and they last forever but they are a different clay body.
I would not prefire.