Breathe …is there anything more important?

7Jul/135

What a difference a clay makes!

I just finished a couple of glaze tests. My goal is to develop a nice matte glaze to add to my palette with which I will be able to use with a variety of clays. I learned how to do this from John Britt's, instructional video, Understanding Glazes. I did a color blend and a triaxial blend. For a base I used a recipe for Val's Turquoise. I fired my samples in an electric kiln and used the firing schedule from Mastering Cone Six Glazes recommended for matte and semi-matte glazes, however, I added 15 minutes of hold time to the max. temperature which gave me a total of 30 minutes of hold time. I made test tiles from both light and brown colored clays. Pictured below is a photo of my triaxial blend. I used three coloring agents: copper carbonate, cobalt carbonate and chromium oxide. I am very happy with the bright colors that a strontium glaze gives and with this knowledge I can now pinpoint the exact color I want to use.

Triaxial Blend

My color blend (pictured below, from left to right: Spanish iron oxide, chartreuse Mason stain, cobalt-tin oxide-chromium, tin oxide-chromium, chromium oxide, rutile, red iron oxide, base only. Notice anything interesting about the samples on the brown clay?

03ColorBlend

 This can be seen better in this closeup, brown on the left and light-colored on the right.

Glaze Test Closeup

Yikes! Is that a major case of brown clay pitting and blistering or what!  Ive been trying to figure out why this happened.  Was it something with the recycled clay that I used? Did the brown clay have too much grog in it? Nope. I ruled this out because I did have a couple tiles of non-recycled brown clay which gave the same results.   All I can guess is that the coloring agent in the clay, which is probably iron, does not like this glaze base and reacts with something in the glaze and volatilizes. If anyone who might be reading this has had a similar experience, or who knows why this has happened, or knows what I can do to make this glaze work for brown clay, please let me know.

Despite the pitting and blistering, this was very fun and interesting. The samples on the light colored clay came out great. They are creamy matte, just what I was wanting.

Many thanks to John Britt for answering my questions and getting me started.

My results were quite a surprise. I thought that I would be able to guess at what the samples would look like on the brown clay. I was so wrong, but this is what makes ceramics so much fun.

Comments (5) Trackbacks (0)
  1. I use Val’s turquoise as one of my standard glazes on both Highwater Redrock (iron red/brown clay) and Standard 266 (black) clay with good results.

  2. How do I follow your blog?

  3. Thanks Nancy, It’s a very nice glaze and glad to hear someone’s getting good results with it. Actually, I just got an email from John Britt and he suggested to adjust my firing cycle. I’ll try again and do that.

    Val, I’m working on it.

  4. I don’t know if you have successfully fired the brown clay at the same cone/temperature+time before or since, but the brown test tiles seem overfired to me, rather than having had a reaction to the clay…

  5. Thanks for comment Roberta. You just might be right. I about to calibrate my kiln to make sure I’m firing to the correct temperature.


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