My experiments with Spectrum’s Mars Raku glaze this month were a little different than some of my past tests.  I love watching old Saturday night live episodes and I have particularly fond memories of a skit with Dan Ackroyd as Julia Child and she makes a mistake and cuts herself while preparing a turkey.  “I’m glad in a way that this happened,” she declares (as she bleeds all over the turkey…you can watch the skit here, if you want.  The fun begins around 2 min in) because it gives her the opportunity to talk about what happened.  Similarly, my firing of Mars did not come out as I expected.  The glaze was actually under-fired.  But I’m glad, in a way, that this happened because it gives me the opportunity to go a little more in depth into the topic of how you know when your glazes are mature AND understanding the hot spots and overall “personality” of your kiln.

When I’m testing a new glaze, I always try to put a piece with some of our crackle white in the kiln where I can easily see it.  I choose crackle white for two reasons.  1. Crackle white doesn’t really have anything in it that will fume onto the new glaze and affect the outcome, and 2. I’ve fired it enough times that I know when it melts and when it’s mature.  So when I’m testing a new glaze, I can find out if its overall melting temperature is higher than the crackle white, lower than the crackle white, or about the same as crackle white.

So what good does this do me?  Well, in subsequent firings of the same glaze, I can make adjustments ranging from placement in the kiln to glazes fired together.  If I know that Mars, for instance, needs to be fired hotter than Crackle white, and Laguna’s Dark Red melts much cooler, I will be unlikely to put them in the same kiln load, much less on the same pot.  (Although knowing me, I’d actually DO that experiment with Dark red on top of Mars, thus fluxing the mars down a little and maybe ending up with something that melts right with Crackle white….but that’s an experiment for another day and on a WELL-kilnwashed shelf!)  But back to the position in the kiln.  I have learned over years of firing the Bracker Raku Kiln that the coolest spot in the kiln is in the far back, and the hottest is right in the front.  Why?  Because the burner goes in the front, under the shelf, the flame hits the back brick and is reflected to roughly the middle of the shelf.  Then the vent holes in the top front of the kiln draw the flame up and out the front, right past any pots positioned on the front half of the shelf.  So, if I were to go back in time and re-create the test firing with the knowledge I have now, I’d put all of the pieces with ONLY Mars on them right in the front of the kiln, and put the other pieces that have the crackle white more in the back.  The Nepheline Syenite in the Crackle White will flux Mars down a bit, so that the cooler temperature in the back of the kiln will be mitigated and the glaze will still melt and mature.

I was very pleased with the results on the pieces that did have the crackle on them.  In the gallery below, I included lots of pictures of each piece from a variety of angles.  I’ll be doing more experimentation with Mars now that I have more information on it.  In the meantime, why not do some experimenting yourself?

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