Identifying Cone 10 Bisque

[creekgirl]

Hi,

I hope someone can help me figure this out!

I have a lot of unfinished bisqueware that's been sitting around for 10 - 15 years that I'd like to glaze and finish.  The clay was mostly purchased from a studio that fires cone 10, and I used to purchase shelf space to fire there.   However there could be (albeit not likely) some bisqueware  in mid-range clay from a studio that fires electric.  I would like to finish in cone 10.  Is there some way to identify cone 10 clay bisqueware from possible mid-fire clay bisqueware?  I don't think the cone 10 studio would even let me fire there unless it's their clay, with good reason, as mid-fire could melt down.   Would they be likely to recognize their own cone 10 clay in its bisque stage?

I know it was stupid to let it sit for so long, but I hate to throw all this bisqueware out.  Thanks for any advice you can offer.    

creekgirl
 

 

[neilestrick]

@creekgirl Sorry I messed this up trying to merge the two threads!

Can you tell that you have two different bodies, or are they identical as bisque?

[creekgirl]

Thanks, Neil.  I can almost identify a timeline starting with the years when I had a raku kiln and used a mid-fire clay body, and some earthenware. 

The white and light pink bisqueware are probably mostly more recent use of cone 10 porcelain and stoneware clays -  put aside as I was mixing up shino recipes for test tile experimentation, which I never got around to firing.  But I made a bunch of bisque fired test tiles I know are the cone 10 clay.  Matching the bisqueware test tiles to bisqueware objects might identify the cone 10 clay.   Maybe the studio would allow me to fire an unglazed bisqueware test tile on a broken slab of shelf to validate their cone 10 clay body.  I don't know, seems kind of unlikely......

creekgirl

 

 

[Rae Reich]

You could break up a representative piece or two, identify bits with RIOx, and fire them at ascending temps (on a waster slab). 

Just judging by bisque color is deceptive, positioning in the kiln will affect color, sometimes looking pinker than white.

[creekgirl]

Interesting.  Thank you, Rae.  Since I have no control over firing, as both mid-fire and cone 10 would be fired at studios in their kilns, would there be a way of viewing ascending temps?

 

"Hope is the thing with feathers that perches in the soul, and sings the tunes without the words, and never stops at all."   (Emily Dickinson)

[Brandon Franks]

1 hour ago, creekgirl said:

Interesting.  Thank you, Rae.  Since I have no control over firing, as both mid-fire and cone 10 would be fired at studios in their kilns, would there be a way of viewing ascending temps?

 

"Hope is the thing with feathers that perches in the soul, and sings the tunes without the words, and never stops at all."   (Emily Dickinson)

Mostly studios will use clay that is bisqued at the same temp throughout. I have a stoneware that I use for some parts of my pieces that get discarded every firing - fires the exact white as my porcelain, so, as Neil said, it is near impossible to gauge the peak temp or the bisque temp by the color.

 

Here is what I would do. Break a piece of every different color clay body that you have. I can see from the picture you provided that there are some pieces that look a little dinged up - chose those ones.  Explain to the studio the situation, and ask them if they could fire shards of your clay (no glaze). At this point, once fired, you will be able to determine if the clay is cone 10, or is a cone 6. Cone 6 clay will melt in a cone 10 firing. It will not cause any damage to the kilns either, the clay comes right off the shelves from my experience.

 

You may also have clay with a wide range of temps, I have used a stoneware that matures between cone 03 and cone 9. Every studio I have been in, the max temp of the clay usually stays consistent so there are no issues with work melting to shelves.

 

If you explain your situation and bring in some small shards (1-2 inches) they will most defiantly understand and fire them.

 

Hope this helps!

[creekgirl]

Thank you, Brandon!  So I guess I should group bisqueware pieces that seem to be of same clay body, choose a small representative broken bit from each group, mark each with RIO identification and have them fired to cone 10 on broken pieces of kiln shelf?

btw..........kinda funny, the "dinged up" bisqueware pieces may be my attempts at a traditional wabi Japanese aesthetic.  I may not be very good at it, but I love that sort of thing!

[Brandon Franks]

56 minutes ago, creekgirl said:

Thank you, Brandon!  So I guess I should group bisqueware pieces that seem to be of same clay body, choose a small representative broken bit from each group, mark each with RIO identification and have them fired to cone 10 on broken pieces of kiln shelf?

btw..........kinda funny, the "dinged up" bisqueware pieces may be my attempts at a traditional wabi Japanese aesthetic.  I may not be very good at it, but I love that sort of thing!

Yes, exactly that. If you have extra clay around, you could make a flat slab and use that to lay, fire, and mark them on, may be easier if you want to look back at it quickly.

 

If you are making a marking liquid, use a "recipe" or else it is really thin and hard to see. I made a batch of like 70 test tiles when I first started doing my new glazing technique, used a thin RiO mark on all of them to differentiate, bug it burned right off - couldn't tell what was what.

 

I now use-

25% EPK (or Grolleg on my porcelain now, but doesn't matter)

75% RiO

 

You can also do cobalt, it is stronger and easier to identify - also quite a bit more expensive for marking things. If you want to use cobalt carb, its 2.5% and 97.5% EPK. For RiO, you may want to do two or three coats, especially on stoneware.