Leaching Test for New Studio Glazes

This quarter began with a great deal of energy in the studio around testing new glazes. Most quarters I have my intermediate class mix and test glazes to give them some experience reading glaze recipes, handling materials, glazing, firing, and analyzing test results. Occasionally I have organized larger groups of students to find new glazes or glaze replacements, or to perform leaching tests.

our glaze test bowls laid out before the leaching test commenced

In 2013 I had a large group of students involved in a leaching test to make sure that all of our studio glazes are food safe. About a year ago, I had two smaller groups of students test and mix replacements for the clear glaze we had been using in the class (it was coming out opaque) and for another class glaze that wasn't giving us the color we wanted. Both of these glazes are now used in the studio in place of the old blue and old clear glazes. As a result of the leaching tests, we have relabeled all of our class glazes and are in the process of phasing out our last remaining decorative glaze that is not food safe but could mistakenly be used on a functional interior.

our leaching test with lemon, detergent and control (nothing)

In March of this year, there was a lot of energy and excitement about testing glazes and replacing some class glazes, especially from my independent students. Early in the quarter, I met with the students to discuss the scope of the project, divide up the work and plan when various stages of the process needed to be done. Most students who volunteered (or, in the case of my intermediate class, were required) to be involved were able to find recipes and mix small batches by the agreed upon date. Most of these were then fired and we planned to meet to discuss the results.

The fourth line of bowls (at top) is in a different clay. Most test bowls are stoneware with the spare in porcelain. The celadon clay bodies are reversed with an inlaid coil of stoneware for two bowls because uniformity is, apparently, too difficult.

For a variety of reasons, several students didn't attend the second meeting. This quarter's independent student cohort has been uncharacteristically incapable of getting along in the studio and some of the drama escaped its bounds that day. I've had patches of disharmony in the studio before, but this year, and this quarter in particular, the situation reached an almost unbearable level. It has since gotten marginally better and we were able to complete the work of the quarter, but I am discontinuing the independent class for a time. Some of the students need to move on and find a new place for their work to continue to grow. Some students simply took advantage of my patience and the studio setup too many times until I finally reached my own breaking point.

washed bowls after the test, can you spot a difference?

Even with the drama of these students this quarter, we were able to successfully complete the planned testing process for five glazes, more or less. All five of the tested glazes passed the leaching test, though one test was a little odd since we appear to have two different colors of one recipe. Next week we will decide whether to incorporate any of the glazes into our studio as new glazes or replacements for existing class glazes. We tested two black glazes, one matte and one gloss. We also tested a celadon, a satin/matte orange glaze and a purple/blue glaze that has been hanging around the studio for some time. We (sort of) performed leaching tests on our new-this-year blue and a Shino that gets used sparingly in the studio.

The two bowls on the end only had one bowl dipped in each glaze so the leaching tests had to be done in stages. The cracked bowl is in celadon as are the others in its line. For some reason one of the bowls is blue, the other is taupe; they are supposed to be the same glaze.

If you like the bowls in this test, some of them will be available for purchase in the clay sale this coming November 2016.