Wednesday, October 13, 2010

Firing to Cone 10

I did a Cone 10 fire with the four different types of paper clay mentioned in my earlier post.

From left, is Gault 10 paper clay, Southern Ice Porcelain paper clay, a red-bodied paper clay, and Black Mountain sculpture paper clay.

These test tiles went through the bisque fire first and then to Cone 10 reduction. Below are the results.

From fresh clay to bone dry greenware:
All showed approximately 4 - 5% shrinkage.

After Cone 10 fire (total shrinkage, from fresh clay to Cone 10 fired):
Gault 10 Pclay - 11.9%
Southern Ice Porcelain (with feldspar) paper clay - 9.4%
Red-body paper clay - 13%
Black Mountain sculpture paper clay - 10.4%

Caveat: The same caveat applies to this test.

Visible change in Cone 10 fire compared to Cone 5.
1. The Gault 10 Pclay turned a deeper buff color.
2. The feldspar crystals in the Southern Ice Porcelain paper clay "popped more. Some specks of iron showed up, and I don't know where they came from. Perhaps, a contaminant.
3. The red-bodied paper clay turned a very warm orange-brown color.
4. The Black Mountain sculpture paper clay turned a very deep brown-black.

At Cone 10, these test tiles were completely vitrified and you can tell the difference in the sound when these tiles were struck together compared to the Cone 5 fired tiles.

On the Gault 1o Pclay test tiles, I decided to also test out some colored slips - blue, green and black.


Phaedra Mastrocola said...

Hi! I'm hoping you can help me. I have a large cone 10 paperclay sculpture to fire. I have never fired paperclay before. I'm advised to fire very slowly.

I am a lower school art teacher and firing knowledge is limited. Would you advise that I use my Skutt ELECTRONIC COMPUTERIZED CONTROLLER to simply select Cone 10 and Slow speed? Or would it be better to select a custom program? I have several slow preset programs, a 14-15 hour one, an 18-23 hour one, a 24-27 hour one. I guess what I don't understand is how the cone relates to these settings. Is it that when firing slow enough you don't have to set the cone?

Thank you in advance for your expert advise.

Happy Holidays!

Anthony Foo said...

Hello Phaedra,
Thank you for visiting my blog. I hope the info here has been helpful. As to your question, yes, it is better to bisque fire slowly. You may use the preset settings on your kiln for a slow ramp up in the temp. You will still achieve the firing temp. It's just that it takes longer to get there and it allows for the temp to rise gradually.
Also, make sure your piece is completely bone dry before the bisque fire. After the bisque fire, you can treat paperclay just like you would any bisqued piece.
Hope this is helpful. Feel free to contact me if you have further questions.

Anthony Foo said...

Dear Phaedra,
You can also do a one fire with paperclay. My comments about the piece being completely bone dry applies. Glazes can be applied on bone dry paperclay and then do directly into cone 10 fire.