For a very long time now I’ve wanted to utilize some volcanic rock as glaze. In much of my research here at Utah State I’ve been looking at iridescent phenomena, both in glazes and in the natural world. It was quite fortuitous, then, when geology grad Doug Jones asked me to accompany him on an excursion just over the border into Idaho to look for Xenoliths, which at this site are very deep mantle rocks that have been blasted quickly to the surface in younger volcanic flows.

While we were poking around looking for Xenoliths, I started picking up some rather remarkable chunks of iridescent vesicular basalt. Vesicular basalt is characterized by it’s frothy, bubbly matrix… if you don’t know what I’m talking about, think red lava rock. It’s one in the same. Here’s an example:

After picking up a good pile of this stuff, we went on to find about 40 Xenoliths, as well as some other interesting stuff.

Once I got back to the studio it was time to figure out if this stuff was even viable. My standard go to for this is to break off a small chunk, put it in a dish, and fire away.

After putting theses samples in a cone 10 reduction kiln and a cone 10 oxidation kiln, it became quite evident that I had something useful.

After deciding that this was a good road to go down, the hard work of crushing and processing this stuff began. I started by breaking the boulders down into gravel sized pieces. These then went into out ball mill. I could have shaved down the time it took to mill this stuff by using intermediate crushing equipment (an impact mill, or hammer mill) but I found it easier in the long run to load up our ball mill and run for about 24 hours, sieve out the useful material, add in more course material, and repeat. By the end of 4 days I’d run all the material through and was left with tumbled lava rock:

Larger basalt mixed with porcelain ball milling medium.

With my material milled down fine enough to pass easily through a 100mesh sieve, I then let it sit for a few days, pouring off the water each morning, until gradually the material became thicker and started to resemble a glaze. Because it was ball milled, the particles were quite small, and suspend really well. The next step was to take this glaze material and see what happens in the kiln. I was quite pleased:

Now that I knew I was dealing with a viable glaze, I couldn’t wait to get this stuff in the kiln and firing it in a weird, experimental reduction cool cycle. Last year I discovered some really incredible surfaces by cooling a kiln in reduction, and holding at certain temperatures. In this case, the geologists have told me that basalt solidifies at about 980C, so I’ve been crash cooling the kiln to around this temperature, holding in a reduced environment, and letting the metallic compounds crystallize in reduction. My speculation is that I can somewhat re-create the conditions in which iridescent phenomena occur. Lo and Behold:

This result is remarkably similar to effects you can achieve in Raku, or Lustre firing… but it’s a different phenomena, and relies on totally different elements; namely, Iron. Whereas raku usually derives rainbow iridescence from Copper and Cobalt, and lustres from Silver, and Bismuth, these colors are coming from Iron with trace amounts (less than .5% Manganese and Titanium). It’s very interesting on the ceramics side, and the geologists are quite interested too, because the phenomena is not wholly understood. One of the perks of being a graduate student with STEM funding is that I have access to fancy analytical equipment. This analysis has allowed me to build a material profile in Insight Glaze Software.

To that end, my future plans with this research will involve more experimentation with the firing process. In fact, I’m currently working on a piece that will exhibit between 10 and 20 wall hanging tiles that all feature the exact same clay and glaze with different firing schedules. At the same time, I’ll also continue to tweak this material by adding other oxides to end up with brand new flavors of glaze.