Sometimes I come across a color I just can't figure out. A few months ago I was asked to make a a light green glaze for an order. Not a problem, I thought, and quickly agreed. I already make a few shades of aqua and turquoise, how hard could it really be to remove the blue and get down to a pretty, bright green? Actually pretty hard. I was dancing with the word impossible for a while, which is of course an exaggeration and also an impossibility on its own-- I see green glazes everywhere-- but I was that frustrated and making zero progress figuring out how to make green for my high fire, oxidation, porcelain and stoneware.
Imagine my surprise when I opened the kiln to find pieces that went into the kiln with a clearly green colored glaze but which came out this color:
While I love this warm, nutty color I've named Cashew, it is not green. Not even a little green. The glaze that went onto the pieces was this color:
See the problem? Understand the shock?
I've been making my own glazes for years and have a general understanding of how glazes work, which minerals and oxides produce which colors in which firing atmosphere; The basics. I think I will always consider my understanding to be general, even years from now when I have a few decades under my belt. There is just so much to learn, and I'm not interested in adding chemistry classes to my To Do list any time soon (or ever). Instead I work with a trial and error approach that feels an awful lot like complete failure, until finally, it works!
Interestingly, the stoneware Cashew bowls were glazed with my Satin Matte base, which is a very, very different formula than my glossy, translucent glaze I use on my porcelain. Because these glazes are so different in terms of their chemical composition, I completely expected the problem to be isolated to my Satin Matte base. I mixed up a batch of green glaze with my Glossy Porcelain Base glaze certain this glaze would work. Instead I pulled from the kiln the tan test tiles below. I'm not sure how or why the glaze pooled purple where thickest.. but that is another mystery for another day. As you can see below I did eventually unload a green test tile from the kiln (yay!) but what a process and hair pulling. I used my Pink Base glaze for the green tile, and surprisingly it worked! What makes my Pink Base different from my other glazes? It's Zinc free. That was the lightbulb moment.
I've known for some time that Zinc doesn't allow for the development of Pink. But green? This was news to me. I also know that Pink can be made by combining Tin (white in powder form) with Chrome (a bright Green in powder form) which is fascinating. These glazes go onto a pot green, but come out of the kiln pink. Mind boggling. Zinc is known to produce brown when used with Chrome (a little fact I'd over looked). So it was a combination of things-- Chrome, Tin (in the form of Zircopax in my Satin Base), and Zinc (in both glazes) that caused the agony. Oh chemistry. I'm thrilled to have finally made a pretty springtime green, and the timing truly couldn't be any better! Just imagine how pretty these bowls will look filled with fresh fruits and veggies! So with that I introduce Spring Green, a new glaze, just in time for summer dinner parties!
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