(2002.04.17)
I've been interested in rutile blue glazes ever since I started doing pottery. In fact, the first pieces I ever threw (those that are glazed) have a rutile blue on them. I've been working on my own versions for over 5 years now, and I think I'm beginning to understand some of what makes them tick. Here's my latest glaze test:
As usual, it provides the occasional bit of oddness (I have come to expect this sort of thing with rutile blues). Here's what it looks like under the stereomicroscope (sorry, monocular view here) --
As you can see, the surface is filled with little crystals, and there are bright glints here and there. Those, I'm afraid, are little cracks down inside the glaze -- not craze-cracks (they don't reach the surface, and they aren't oriented perpendicular to it), but rather some sort of weird thing that happens down inside the glaze, apparently in the glaze-body interaction layer; I think they may be some sort of thermal-expansion mismatch that occurs down there, for reasons I do not understand -- I've calculated the glaze recipe to have thermal expansion that matches the thermal expansions of ordinary porcelains, and it is sitting on just such a body. There's no guarantee, of course, that intermediate compositions will have the same expansion, but I almost never see this sort of "flitter" crack with other glazes. So go figure. I should perhaps note, btw, that this is glaze version F0 in series XIV... I could probably have gotten more information quicker by being somewhat more systematic, but in fact I haven't actually made every single version of every series (far from it -- in fact, I think F0 is the first glaze I've made in series XIV, and I'm not sure whether I made any of the ones in series XIII... perhaps just one of them...), and I have ended up with quite a few interesting glazes, some of which don't look even remotely like this one.
I see a lot more of the star-shaped crystals in this particular test than I usually do, and I'm thinking about making up a formulation that is intermediate between this one and one of my others, to see whether I can control them. I think I'm now at a point where I can control the creaminess of the glaze moderately well, and the thermal expansion, and possibly the depth of color and the amount of purplishness. These are all Good and Necessary Things. I'd like to be able to control those flitters, too, because there are times when I want to have them and times when I don't; but they have eluded me thus far. (Working on it...) There is also the issue of the color that the glaze gets where it is very thin. The best of them achieve a sort of goldness that I really like. As to the worst, let us merely say that I tend to abandon those formulations.
If anyone is interested, I have a few other pages about these glazes: this one, from 1998, shows a version that had just about the best colors I've been able to produce so far (unfortunately at the wrong thermal expansion... sigh...), and this one has some slightly more recent work, along with a photo of the first rutile blue glaze I ever encountered, Larry Bruning's "Opal Blue", on a ridiculously early piece of mine. I typically spray these glazes on, because that gives me some effects I don't get when I use other methods, but the early piece is dipped.
The 1998 page has a link to a page with photos of a dipped bowl that has one of my glazes on it, and this page shows a glaze that's related to the rutile blues that I applied to the piece quite literally by hand.
(More as it happens, possibly on this page, possibly on
subsequent pages.)
Pseudo-mailto: jon [at] bazilians [put it here] org or
jon [at] joss [same thing goes here] com
Last modified: Wed Apr 17 00:27:48 PDT 2002