September 22nd, 2012

Followup to Resounding Failure: Potential Success

I’ve done some work on the problematic Rutile Blue glaze that I wrote about a few days ago, and I thought I should provide a bit of an update. As background, here are photos of test tiles from the first and second firings of the problem glaze, so you don’t have to go back to the other posting to see them:


These are the same glaze, fired in the same kiln under similar conditions, and I’m still not entirely sure what made the difference here; but either way it is clear that the CTE (Coefficient of Thermal Expansion) of the glaze is too low. I like the look of that first tile, though, so I decided to see whether I could achieve a glaze with similar appearance, but without the bad behavior. There was no guarantee that this would be possible, but I thought I had a fair chance: I’ve made other glazes that were along these lines. In fact, I have fired over a hundred Rutile Blue tests during the past ~16 years, and I have lots of test tiles (and recipes), with varied characters. I looked through them and decided that this one —

— would be a good candidate to combine with the problem glaze. There is some blue in it, and although it slid a little on the tile, which indicates a melt with low viscosity, it is neither badly pinholed nor crazed.

I wrote out two new recipes. Version 0.2 is 2 parts of the problem glaze to 1 part of this slightly older glaze, and v0.3 is 3:1. The pure averages were a bit messy, so I tweaked them until they felt right (I think I’m not going to try to explain that here and now), and then I mixed up a test batch of each. Here they are, after a firing to cone 10.5 or so in the gas kiln, the night before last:


[The color balance is a bit off here; the background should be almost a neutral gray, and the glazes perhaps a bit more purply.]

Version 0.2 [2:1] is just beginning to slide where I double-dipped it, and is badly pinholed (this is a common problem with glazes that contain Rutile), but otherwise I like the way it looks. Version 0.3 [3:1] is quite acceptable, though perhaps a bit less exciting. I averaged the two recipes and tweaked the average to increase its thermal expansion just a bit more; I will fire a test when time & tide permit. Once I’m sure I have a recipe that is good, I will convert the existing bucket of v0.1 into a larger batch of the improved version. With any luck, I will have an example in the Art Show at SFContario, in November.