Clay Testing (The Beginning)
So I have been on the search for a cone 10 reduction clay body that fires super dark for a while now. Only recently have I really ramped up testing to actually use it as my primary clay. Another addition to this is I would love to add local/ found material (clay) into the recipe. Ive been working with an iron rich clay dug near my childhood home in Pennsylvania since college. I use it as a decorative slip, it adds such a cool variation of color underneath my satin white glaze. A reason for the interest in local material additions is that I feel more connected to the land around me as well as more connected to my work. The understanding of materials and knowing all of the work that goes into processing the materials gives a greater appreciation for the finished piece.
The search for a dark colored clay comes from all of the wood fired pots i’ve admired for so long, especially when they are decorated with a light glaze or slip. The contrast of a sugary white/ off-white body with a super dark base peeking out is a look that I can’t get enough of. I want to bring this aesthetic to the rest of my work. I like where its at now but, as always, its a stepping stone to the next variation. So with that in mind I began adding more and more tests into the gas kiln to hopefully reach those next steps
When I first began the the search for a darker clay I began with commercial clay bodies. I wanted to see if I could find a commercial clay and incorporate my PA clay into it to achieve my goal easily. Despite many trials I either couldn’t achieve a desired color, all being relatively close to the same color clay I was already using. Or I had technical issues such as bloating or excessive dunting. Since I didn’t know the ingredients of the commercial clay I was lost on how to fix these problems. It was also a bit discouraging knowing a main component in the clay body (the commercial clay) was essentially a mystery and therefore couldn’t fully control all the ingredients. So the idea of mixing commercial clay with my wild clay got scrapped.
Next would be to start from scratch and make a recipe from all dry materials. This is leading up to the more current experiments. I started simple and had made a recipe that was 50 percent fireclay (Hawthorn Bond) with 50 percent PA clay. After the firing I was actually very pleased with the color! It was a beautiful dark brown with a small hint of purple in it. It had fantastic speckling and had decent working properties. Sadly, same as before, there were still bloating and dunting issues. What I had yet to learn, and am still learning, is that the recipe I made was not formulated in a way that it could withstand thermal shock from cooling. The recipe had too much free silica, and without a feldspar to dissolve the silica, it promoted dunting. All being said I still have a lot to learn with the chemistry of firing but I did create a few more clay body recipes based off of these past issues.
50% Hawthorn Bond Fireclay + 50% Unami Creek PA Clay
The new recipes i’ve created still follow my checklist for a custom clay body:
Incorporate local/ found materials/
Rich dark color
Withstand high fire temperature and atmosphere
The following are the recipes and variations I have created so far:
#1 Unami Creek PA Clay 50%, Newman Red Fireclay 30%, C&C Ball Clay 10%, G200 EU Feldspar 10%.
#2 (Same as #1) added 5% grog
#3 Unami Creek PA Clay 40%, Newman Red Fireclay 40%, C&C Ball Clay 10%, G200 EU Feldspar 10%, +3% Bentonite
#4 Unami Creek PA Clay 45%, Newman Red Fireclay 27%, C&C Ball Clay 18%, G200 EU Feldspar 10%
#5 (Less Iron) Unami Creek PA Clay 50%, Newman Red Fireclay 20%, Hawthorn Bond Fireclay 10%, C&C Ball Clay 10%, G200 EU Feldspar 10%
#6 (Shop Clay Variation) Foundry Hill Creme 32%, Newman Red Fireclay 32%, C&C Ball Clay 21%, G200 EU Feldspar 10%, Unami Creek PA Clay 5%
Within the last few weeks (End of September 2022 to current October 2022) Ive mixed up each recipe, tested some simple wheel throwing properties, and made several test tiles of each. The intention is to get as much information out of this weekends gas firing as possible knowing we won’t have another one for another couple of weeks. So each test will showcase what happens to the recipe in hot and cold spots, how it reacts with my decorative slip over top, how it reacts with a wild kaolin i’ve found here in Vermont, how the recipe reacts with my satin glaze, and a mixture of them all together. The recipes are very similar for the most part. Playing off of the proportions of each material in slight variations will hopefully give me insight as to how they react in the basic clay body. Im hoping at least one of them comes out to be promising. Although as I navigate through the creation of recipes, studying materials, and testing, I am realizing how much is still out of my hands as well as how many variables can change even a stable clay body to create problems. Its a blessing and a curse to be working through testing but it is extremely rewarding when promising results come out. Maybe when I open the kiln everything will fall into place and ill be set but lets not get our hopes up. A dude can dream though!