In this blog post I will show the results from first round of tests with a granite from Devil’s Playground in West Utah. In my next blog post I will show the steps getting to this point: how I processed the rock into useable fine powder.

I am currently at Utah State University working towards my thesis show which will be up in the Tippetts and Eccles Gallery next April/May. The plan is to present pots dressed with a variety of glazes made from this Devil’s Playground granite. I want to make 4 or 5 distinct glazes with at least 50% of this granite. The tests presented in this blog post are just the beginning. I anticipate several more rounds of testing and honing in after this.

Lets start with this video that describes this initial round of tests and findings. I found that filming my test results was a more satisfying way to document them rather than just flat photographs.

I dipped 4 small test tiles and one larger extruded test tile in each individual glaze formulation (100g dry material topped up to about 160ml glaze). The tests were all fired to cone 10. The larger extruded tile and one of the smaller tiles were fired in a gas reduction blaauw kiln, one went into a gas kiln fired in oxidation and then one went into a soda kiln that was fired in a neutral atmosphere with a natural cooling cycle. Here is a picture of some of the tiles in the soda kiln…

Now I will list each set of tests. Firstly here’s the tests where I add iron. In the photograph below I ran two similar but different tests. To the set on top I added red iron oxide to 100% Devil’s Playground granite (DP) in these increments: 0.25%, 0.5%, 0.75%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 20%, and 30%. So each test has 100% DP granite plus these percentages of iron.

I used a different base for the lower set in this photograph. Instead of 100%DP granite I chose a previous formulation — DP31 — which is 80% DP granite, 10% lime and 10% minspar. I added the same % additions of yellow iron oxide to this base. The difference was quite remarkable. The lower set were more responsive and produced more varied and interesting results. Talking with John Neely he said that the difference in color response was due the addition of lime and minspar rather than the difference in yellow to red iron oxide. He said that the yellow and red iron oxide should act the same when fired. I want to do a further test to confirm this.

Overall I was particularly into the tests in the lower set with iron added between 3-7% and plan on expanding this test area. I also plan to make a quadraxial blend of the DP granite with one corner being higher silica, one higher alumina and one higher flux with 3,4,5,6,7% iron added across all of the tests. This will show me how the iron content and color is affected by fluctuations in silica, alumina and flux content.

In this next test I added a local red clay from porcupine dam to Devil’s Playground granite (DP) in these increments: 0.25%, 0.5%, 0.75%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 20%, and 30%. So each test has 100% DP granite plus these percentages of red clay. I expected the additions of red clay to have more of an impact. I found that this local red clay, whilst being red, actually did not have that high a percentage of iron in it.

In the test below I did a line blend between the DP granite and a basalt collected from near Craters of the Moon in Idaho. On the left is 5% basalt to 95% DP granite, and then with each subsequent test I add 5% basalt and remove 5% granite. All the way to the right is a 50:50 blend of basalt and granite. I expected this test to produce greater variation. Most of these tests looked like persimmon or kaki glazes. I would like to use some of this basalt to create an iron rich glaze, such as a tenmoku, so want to test more in this area. I will try to add some iron to these tests and try some other tactics too.

In this test I added talc to the DP granite. From the left I added 2% talc, then 4%, 6%, 8%, 10%, 12%, 14%, 16%, 20%, 30%. As you can see the talc lightens the glaze and also makes it more opaque and matte.

In this test I compare washed and unwashed wood ash additions to the DP granite. From left to right is a line blend going from 95% DP granite with 5% ash to 50/50 granite and ash on the right. The washed and unwashed ashes acted very similarly. At about 25% plus the glazes became quite runny. The biggest difference was that the unwashed ash tiles developed an orange halo line under the glaze line. The washed version did this partially but not as pronounced or bright. Unless I really wanted this orange mark then I think I would opt for washed ash as it is less caustic in use.

I did enjoy the light bright glaze that resulted from DP granite plus 15 or 20% ash. I will definitely pursue this in further testing.

This test was adding a ryolite to my granite as a line blend. The results were unspectacular so I will not pursue this! I got similar results when running the same test with nephrite tuff addition.

In this test I added titanium dioxide to my base DP31 glaze (80% DP granite plus 10% lime and 10% minspar). I added 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 20%, and 30%. Up to 6% the glaze just tends to get darker and richer but then from 7-10% you get some pretty interesting and varied surfaces. 20% was curiously lighter blue and then 30% a tan color. I want to do a further test that fills in 11-29% to see this change play out. I do see some potential in these glazes, especially in soda, as the glazes look quite varied depending on how much soda hits them.

Thanks for reading!

I’m in England right now but when I get back to Utah I will get stuck into running the second round of tests and post about the progress.

But in my next blog post I will show how I turned my granite rocks into powder fit for making these glaze tests!