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JeffTimothy

Thoughts On Underfired Bisque

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Hi there,

I'm new to the forums, have been lurking for a while but finally decided to sign up and add one more username and password which I will have difficulty remembering to my long list of the same... :)

 

I've been doing pottery on and off for years but only recently have I finished (almost finished) setting up my new studio space and decided to pursue pottery full time.  I'm the type that likes to jump into things with both feet and as such have just completed my first bisque firing in my new-to-me kiln.  It's an old cone arts kiln with a kiln sitter.  It underfired as I didn't have the sitter adjusted properly.  It fired approximately 2 cones too low.  Fired to about cone 06 when it should have fired to cone 04. 

 

My quesiton to the experts here in the forum...   What are your thoughts on glazing and firing underfired bisque in electric cone 6 ox.  I'd prefer to not have to re-bisque fire.    My only thoughts are to be concerned with my glaze application being too thick due to the under-vitrification of the body and maybe to consider a slower firing schedule to be sure the bisque has off-gassed as much of it's carbon content as possible before the final glaze fire temp?

 

Am I heading for a kiln full of offerings to the kiln gods?  I've always had others to help with the firing so at this point, the science of firing is all new to me.  Just the way I like it.   :)

 

Thanks,
Jeff.

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Guest JBaymore

Jeff,

 

Sounds like you understand the variables well and are preparing to adjust your next steps accordingly.  Go for it.

 

And welcome to the Forums.

 

best,

 

....................john

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would dampening the ware before glazing it help?  if you are dipping the pieces in a bucket of glaze this technique may help. quickly dunk each piece into a bucket of water and pull it out.  line up the pieces in order so that when you finish wetting the last one, the first one is ready for glaze.  go down the line in order so they contain approximately the same amount of dampness. this step seems to prevent the heavy sucking of the glaze when you dip the piece.  that is hard to describe but if you have experienced what i am talking about, you will understand.   

 

did this in the past when i bisqued to 06 and it worked.

 

if you are applying glaze with a brush, i have no experience except when applying some glazes to very dry bisque, finding the brush stuck to the bisque like a tongue sticks to frozen metal.

 

are you using regular small cones or mini-bars in your sitter?

JeffTimothy likes this

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would dampening the ware before glazing it help?  if you are dipping the pieces in a bucket of glaze this technique may help. quickly dump each piece into a bucket of water and line up the pieces in order so that when you finish wetting the last one, the first one is ready for glaze.  go down the line in order so they will be approximately the same.  

 

did this in the past when i bisqued to 06 and it worked.

 

if you are applying glaze with a brush, i have no experience.

 

are you using regular small cones or mini-bars in your sitter?

 

The glaze I'm using is normally brushed on with 3 coats so I think I'll have a bit more control over it as opposed to dunking.  Last time I glazed something that was slightly damp, the glaze just ran off in the kiln so I'm hesitant to try out your technique.  I guess it would depend on the glaze and body.  So many variables...

 

I'm using a small cone in the sitter.  The sitter was definitely out of adjustment.  As I purchased the kiln used, it happened to be missing it's little metal adjusting plate which is used to properly set the bar and weight position.  So I had no idea it was so far out.  I'm luck enough to live 35 minutes from Tuckers Pottery (the makers of the Cone Art brand of kilns.) I spent some time over there speaking with them which helped out.

 

Thanks for your input.

Jeff.

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JeffT;

What is the reason for bisquing at Cone 04? I commonly bisque at cone 07/06.

If you bisque too hot, your glazes won't adhere to the pots.

A lower temp. bisque also save you time and electricity. Ask around to find out why a cone 04 bisque. It'll be worth it to at least know your reasons for this temperature.

TJR.

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JeffT;

What is the reason for bisquing at Cone 04? I commonly bisque at cone 07/06.

If you bisque too hot, your glazes won't adhere to the pots.

A lower temp. bisque also save you time and electricity. Ask around to find out why a cone 04 bisque. It'll be worth it to at least know your reasons for this temperature.

TJR.

 

The temperature was simply a recommendation based on the clay body I was using.  Who knows, maybe this accidental 06 bisque is a blessing in disguise.  I may find after glazing and firing that it's a perfect bisque temperature.  Guess I will find out soon enough.

 

Jeff.

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JeffT;

What is the reason for bisquing at Cone 04? I commonly bisque at cone 07/06.

If you bisque too hot, your glazes won't adhere to the pots.

A lower temp. bisque also save you time and electricity. Ask around to find out why a cone 04 bisque. It'll be worth it to at least know your reasons for this temperature.

TJR.

 

The temperature was simply a recommendation based on the clay body I was using.  Who knows, maybe this accidental 06 bisque is a blessing in disguise.  I may find after glazing and firing that it's a perfect bisque temperature.  Guess I will find out soon enough.

 

Jeff.

 

Jeff;

Sometimes in life you have to ask yourself;"Why?"

It doesn't hurt to ask. There may be a great reason to fire to cone 04.I don't find it necessary, though.

TJR.

YOU DIDN'T MENTION [sorry,caps lock on]. at what temperature you are glaze firing to.If rakuuing, you would bisque a little harder.

T.

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Let me share what I just recently experienced. The instructor did a bisque at cone 010 (found out later it could have been 012) because her other class was going to do a saggar firing. So-o-o-o-o, I placed 23 tiles (3x3), 2 trays and 2 vases to be bisqued --I was NOT going to do a saggar firing. Clay=112 (with specks)
Then, I glazed the 2 vases with clear and glazed the upper 1 inch with red and the 2 trays with clear also. Well, they all came out looking as if I glazed them with puke (yellowish, tan) and the red was very spotchy. I have had great success with clear over 112. At the time, I wondered why my glaze experienced classmate didn't put any of hers in there. Now I know. I was going to experiment with my own underglazes on the tiles and hang them on copper wiring and attach them on a real cool rod. But, my 'testing' is going to be all for nothing because it won't be a true outcome since they weren't fired high enough ( they are red clay). Maybe I could re-fire them at 05 and then continue? I am going to attempt to include photos.

post-15768-0-16916900-1380738121_thumb.jpg

post-15768-0-16916900-1380738121_thumb.jpg

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