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Firing question-- Black clay at Cone 5


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Hi. First time posting. Hope someone can give me some insight into a question I've been struggling with. 

My Ceramics class creates a large scale project using black clay, with no glazes.  We first bisque the pieces at Cone 06, sand them, and then fire them again at Cone 5 (Cone 6 is stated on the box and produces a nicer black colour, but also lots of bloating).

The last time I fired at Cone 5, I used a slow bisque setting. I came back to find an error code on the kiln which basically stated that I'd overheated the control panel. Luckily everything still came out fine, but I want to avoid this happening again because I'm afraid of damaging the electronics. 

I'm wondering if the length of the bisque fire caused this, and if a slow glaze fire setting would be preferable. Does it matter, considering these pieces have already been bisque fired once? Any other tips on how to avoid the panel overheating? 

Thanks! 

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You need to have a long firing with  black clay it does a lot of off gassing,  you also should bisque at 04.   Which brand of black clay are you using?  I use black clay for small projects but I am about to run out.  The clay I used was made locally but was discontinued when the factory  was sold.   A small fan blowing  on the controller box might help,  you probably need the controller checked out.   Denice

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Do you have a record of what point your last cone 5 firing errored out at?Are there other factors may have contributed to the panel overheating? Is your kiln in an enclosed area that retains heat? How ventilated is the space? If you’re using pre-programmed firing cycles, what’s the model of the kiln? We can have a look at the ramps and holds and see what the differences are between the cycles and give you a better answer. 

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12 hours ago, JiyaiFora said:

I came back to find an error code on the kiln which basically stated that I'd overheated the control panel.

Hi and welcome to the forum!

Most controllers have the maximum board temperature at 160F (plus or minus 10F) so either the board exceeded this or someone has changed the max temperature it can reach before the controller shuts the kiln off. Have a look at your manual to check how to see what board temperature is set at.

Re black clay firing, have a look at the chart here, particularly the 600F - 1650F section, this needs to go slow to burn off the volatiles in black clay. Also, don't go past cone 5 if there is a high level of manganese in the clay (which is in most cone 5 bodies) as others have said.

(moving this over to the equipment section)

Edited by Min
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