Thursday, October 14, 2010

Paper clay and Wire Mesh - Part 2

This project with paper clay (Southern Ice Porcelain) and wire mesh did not work out.

The picture to the right showed my original concept.

The paper clay encased wire mesh survived the bisque fire quite nicely, but did not fare well at all at Cone 5. The black pods on the inside have been fired to Cone 10 and are there for "dry-fitting."

The "pod" collapsed under the weight of the paper clay; the additional weight coming from the "thorns" I added as shown in the bottom picture. A kiln shelf (illustrated by the white box) stopped the piece from falling completely over.

One thing I learned from this is that the shape of the wire structure is important and how much additional load from the paper clay must be taken into account.

Firing to Cone 5 was too hot for the wire mesh to survive as it completely melted and black gobs oozed out of the cracks in the paper clay and re-hardened.

Paper clay and Wire Mesh

I decided to make a simple bowl out of the the remnants of some steel mesh (also called chicken wire or hardware cloth) I had laying around. I have actually come to enjoy creating these wire structures/sculptures. I can be a pain - literally - when your fingers get poked by the cut wires. Working with gloves just does not do it for me so it's just my bare fingers, a couple of pliers and patience.

The completed wire structure was dipped in Southern Ice Porcelain paper clay slip repeatedly until I was happy with the thickness of the coating achieved. Close attention was paid to the lower half of the bowl so it got more dips then the upper half to make it more stable.

I test fired this to Cone 5 in an electric kiln without doing the bisque fire. No glazes were used.

1. Due to the simple construction of the bowl, this piece survived the Cone 5 rather well.
2. There were several cracks in the clay and the melted wire oozed out.
3. At Cone 5, the wire is completely melted, so it's looking for a place to escape and run out. Cracks in the clay provided this outlet.
4. I think the cracks cannot be avoided as the pressure from the melted wire will find the weak points in the clay coating and burst out.
5. Another test would be to fire to Cone 1 (avg. 2072 degress F) vs. Cone 5 (avg. 2163 degress F) for example, and see how the wire survives. At bisque temp. of Cone 04 (avg. 1943 degrees F) the wire is intact.

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.

Cone 5 with various Paper Clays

I made test tiles from 4 different kinds of paper clay. From left, is Gault 10 paper clay, Southern Ice Porcelain paper clay, a red-bodied paper clay, and Black Mountain sculpture paper clay.

All three paper clays except for the Black Mountain sculpture paper clay were commercially purchased. I added the paper pulp into the Black Mountain clay to make it into a paper clay variety. I made a couple of changes to the Southern Ice Porcelain paper clay by adding feldspar crystals to it for one of my earlier projects and to the red-bodied paper clay, I decided to add more paper pulp into the already made paper clay.

The test tiles were marked off in one inch intervals for a total of six inches. This will enable me to calculate the shrinkage during drying and after firing. These tiles were fired ONCE, from dry greenware to Cone 5, without going through the bisque stage. I wanted to try out this one fire approach.

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

After Cone 5 fire (total shrinkage, from fresh clay to Cone 5 fired):
Gault 10 Pclay - 10.9%
Southern Ice Porcelain (with feldspar) paper clay - 8%
Red-body paper clay - 12.5%
Black Mountain sculpture paper clay - 10.4%

Caveat: These test tiles were made and fired flat in the electric kiln so the shrinkage values reflect the manufacturing and testing conditions. I did not test for vertical shrinkage. Adding the feldspar crystals into the Southern Ice Porcelain paper clay may also have affected the shrinkage since this clay showed the smallest amount.

I also made small pinch forms from the above four paper clays and fired them to Cone 5 (one fire) together with the test tiles. The result from the one fire test showed that I can easily fire to Cone 5 without any problems.

Why Fire to Cone 5?
For my sculptural pieces, I really don't have to fire to Cone 10. The higher cone puts more stress on the clay structure and provide more opportunities for the work to wrap, sag, or even fall apart. Granted that at Cone 10, the clay will be vitrified and stronger.
Another good reason is it is more energy efficient to go only to Cone 5. The ability to do a one-fire with paper clay also reduces the energy consumption since I don't have to do a bisque fire.

Tuesday, October 12, 2010

Save That Cardboard

I think as artists we find many uses for every day things. Take for example, cardboard boxes that things come in. After being cut up into flat pieces, they make great "trays" to carry my paper clay slabs from my studio to dry outside in my patio.

A few weeks ago we had a few days of rain following a week of very hot weather. I was in the middle of making a rather large vessel and did not want to wait for it to dry on its own time so I made a "drying box" out of the sheets of cut-up cardboard. All the pieces are held up by their own weight pressing against each other. I did not use any tape. A small bathroom heater (running for about an hour at maximum power) provided the heat to firm up my work sufficiently enough for me to continue working through those couple of rainy days. I put my work-in-progress vessel into my make shift "drying box" as needed, each time rebuilding the box. The Sun came out after two days of rain.

It makes me appreciate how much "free power" we get from our Sun on a typical Southern California day. When it comes to paper clay, the Sun is our friend! I did a search on Google and found out that on a sunny day, we get on average 100W of solar energy per square foot.