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Do I Need To Re-Bisque?


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I did a bisque fire last night in my 40litre electric kiln with sitter and digital controller. Digital controller set to finish at 1000 oC. 03 minibar in kiln sitter. I grabbed a cone pack from my shelf (don't often use these!) and placed it in the Middle shelf.

 

This morning, kiln off and cooling. On opening the lid, the bowls all look fine - 2 different types of stoneware, but none of the cones shows any sign of bending.

 

When I checked, I had used 03 04 and 05 cones which I'd prepared for an earthenware glaze firing. So my dilemma now - Is the work bisqued enough? Do I need to re-bisque to a higher temperature on the controller? Why didn't at least the 05 cone bend a little if the kiln reached 1000 oC as programmed? As I've never use cones in a bisque firing before and only a couple of times in glaze firings, I can't compare this to any other firing, perhaps all my previous bisque firings have been the same without me realising???

 

I'd welcome anyone's thoughts on this.

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If your bisque under-fired your preferred temperature, then it might be more porous when applying glaze. Do you need to re-bisque; no. If you dip for glazing, just be careful of how absorbent the wares are; a more porous item will absorb more water (and glaze) when dipped -- which could lead to glaze runs in the glaze firing. Glaze a piece, then adjust your dipping time, etc. accordingly.

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If you tap them and they ping, they are bisqued. It is not crucial to bisque to an accurate cone temp., but it is for glazing. They may be a little porous, but if they are not grey, they should be fine.

There are a lot of potters who just bisque to a good red colour in their kiln and shut her down. No cones at all!

You might have a burned out element if it isn't reaching your desired cone.

TJR.

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C06 is about the 1000Deg C so the C05 wouldn't be bending if your normal bisque firing schedule was adhered to.

I fire bisque to C06,   C08 used to be the go with lots of potters so as Bciske suggests, if your bisque firing is usually higher and your glazes are mixed to accommodate that, then you'll have to test how your pots take up the glaze,

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I did a bisque last weekend in a manual kiln with kiln setter and timer as shut off's

I set an 08 cone in sitter forgot  about resetting the timer. Started it at noon took my wife out to dinner and at 8pm noticed the kiln was off. I thought wow a fast fire considering the full load. Turns out the next day the timer shut the kiln down way before 08-most of the wares where white and rang fine some where not as white but fired. Last temp I saw on pyro was 1200 degrees. These non white pots really will suck up glaze so I glazed them faster.

I would guess your pots are just fine.Just pay attention on how they take glaze.

You should use cones as well until you know whats going on.

Mark

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Thanks for all your reassurance - have just managed to take a better look at the pots (grandma duties yesterday & overnight!) and they seem ok to me and just about 'ping' Joel. I'm used to a more resonant sound with my white earthenware, which I throw/trim very thin. Have only just moved to try stoneware so I don't have much of a benchmark to go on at this stage. As you say bciskepottery, TJR and Babs, I'll be vigilant when glazing.

Mark - my first thoughts were exactly that - "had the timer shut the kiln off?" - but there was still some time to go, even though I had, like you, forgotten to reset the timer. Another lesson learnt even though it wasn't today's problem!

If it hadn't been for the cone pack, I wouldn't have given it a second thought, but I think I'll now use cones for the next couple of bisques so I can see exactly how the kiln is firing at the lower temperatures. Babs - I did look up all he cone temps afterwards and had ascertained, as you say, that 1000oC is around the 06 mark, but I thought that in that case, the 05 might have shown just a little sign of bending? - or are the margins narrower than that?

It's so helpful to be able to stick up a post and get some instant feedback - thank you all!

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