Putting these reports on the Web should facilitate distribution, and will make it unnecessary for me to send out overly long email messages. It also provides an automatic archive.
Just before the NCECA conference this year, I was privileged to take a workshop with Ruthanne Tudball, who came in from England. Her work is entirely different from mine, and it was a real trip to watch her and talk with her.
Ruthanne spent most of her first eight years as a potter self-taught, in a tiny basement workshop that barely had room for a wedging table and a wheel, so she was unable to fire her work. She’d make something, and put it into the scrap bucket so she could recover and reuse the clay. She couldn’t afford to get attached to any of her pieces. I find the whole business kinda staggering.
NCECA itself took place in Baltimore, in March. As always, it was very good. I got to talk with some extremely knowledgeable people, and picked up good information on several subjects. I also donated pieces to two of the benefit auctions, and participated in the Clayart mug exchange. (Clayart is a mailinglist on the Net.) Several folks also asked me if I’d exchange pieces with them on the side, something that hasn’t happened to me much in the past, and the Clay Times folks told me that they’d have been happy to have one of my pieces in their 10th Anniversary show, which I unfortunately didn’t know about in advance (they were in something of a tizzy, and missed notifying some folks). Too bad -- I’d have been in rather august company. Either way, though, I take these items as an indication that my work is improving, and that it is attracting some notice, both of which are very good.
Jesse Hull, at Red Star Studios, in Kansas City, is planning a large exhibit of crystal-glaze pieces, to take place later this year. As part of that exhibit, he will be running a workshop, on Labor Day weekend. I apparently came to his attention when I put a photo of a fluorescent piece on Fa Shimbo’s Bulletin Board for crystal-glaze potters, and I am now an invited participant in the workshop. This is too cool for words.
I cautioned him that I rarely do zinc-silicate work, and he’s entirely cool with that. In fact, it’s part of why he wants me to be there.
I have essentially finished an article on Fluorescent Glazes for Clay Times Magazine. It should appear in the May-June 2005 issue. I didn’t get quite as many photographs as I’d wanted, but I can include a few extras on the Web page I’ve written about how I took the photos and why it was fraught. (You can find that page here, if you’re interested.)
In the process of creating material for the article, Fa Shimbo and I worked to improve the calcium tungstate glaze that I made when I wanted to see the green fluorescence of erbium. We got something pretty good, which I’m currently refining further. I have tentatively called it "SnowCaT", because it looks like a window into an impossibly heavy blizzard, with a good deal of depth, and because of the crystals that are causing that effect. This glaze, particularly the pink version (with 4% Er2O3 added to it), attracted a little bit of attention at NCECA. The article will contain the recipe as it existed at that time, one revision away from the one that Fa and I built in Colorado in February; but I have seen some delayed crazing on at least one test tile, which is why I continue to mess with it.
A few months back, I dipped one edge of an early CaT test tile into a solution of europium nitrate. Where the dip and the glaze overlapped, the fired tile has a region that’s an odd orangy brown. A few days ago I decided to see whether there was anything interesting to be had from this, and I added 1% Eu2O3 to a SnowCaT test that I fired in reduction to Δ 10. Sure enough, it turned out a pale but pleasant yellow-orange. The colorant appears to be opaque, so it will be of somewhat limited utility; but it is a color that we don’t often see in high fire glazes, and may be of interest to some people. Moreover, when I added 6% Er2O3 to the glaze in addition to the europium, I got something that rather resembles peach sherbet and is pretty nifty.
I tried 2.5% Eu2O3 in the next version of the glaze, and the color does intensify slightly. I think it also becomes a bit more brownish, but I’m not really sure. In any case, further testing is clearly indicated. With some luck, I’ll get a short note out of this, in one of the magazines.
Meanwhile, it occurred to me that I should try the same sort of thing with molybdenum in place of tungsten. Calcium molybdate occurs in nature as the mineral Powellite, which tends to exhibit a buttery yellow fluorescence under shortwave UV. (The corresponding W mineral is Scheelite, which fluoresces sky blue, also under SW UV; it is more or less inert under "blacklight".)
I don’t have any MoO3 at the moment, so I used ammonium molybdate, which happens to be soluble in water; some of it migrated from the glaze into the porcelain test tiles during drying, and when I fired the tests in moderate reduction, it did something I was not really expecting: the glaze is a milky clear, but the porcelain under it and wherever else the Mo ended up is a nice inky blue-gray. This is a pleasant effect, and we will have uses for it.
If you want to see photos of these test tiles, you can find them here.
I am in the process of setting up two electric test kilns. One will be extremely small, and will plug into a regular wall socket. I will probably run it off a Variac, so I can regulate the rate at which it heats and cools, unless I get ambitious and learn how to use the nifty little controller that Howard Davidson sent me a while ago.
Either way, the kiln will use a Type S thermocouple; if I’m not running it with the controller I have an Omega readout, recently acquired on eBay, that will let me see the temp. (Type R and S thermocouples are good for relatively high temperatures, but they have very low output levels, which require amplification. Potters generally use Type K TCs, which have huge output and do not require amplification, but they become erratic over about 1100° C, which is a pain in the butt. I’ve had Δ 9 firings in my regular electric kiln finish with indicated temperature of 1160° C, and I’ve had them finish with indicated temperature >1300° C, essentially off scale on the pyrometer. This just doesn’t cut it.)
The other kiln involves one section of a 23" kiln, and will run on 208 VAC. I’m hoping to use a thick floor and extra insulation on the lid, and I may even wrap the kiln ring itself in fiber blanket, so that it will reach cone 9 without straining.
Earlier this evening, while I was moving firebrick and other bits for the tiny kiln, I looked at my old Cress kiln, which blew its heater element a while back. I’ve been holding off on replacing the element, partly because they want $65 for a new one (they recommend replacing the little ceramic rods that help hold it in place, which increases the price), and partly because I’ve been busy with other things. Tonight, however, it seemed like a good time to investigate. I was lucky: there was only one break in the element, so I took a small piece of high-temp wire that I’d clipped from the end of another element, and stuffed it into the region where the break is. This is rude, crude, boorish, etc;, and I don’t know how long it will last; but I have already been able to do a china paint test firing, which is what I want to use the Cress for in any case it is extremely small inside, and it is only good for about 1000 celsius.
The china paint test was apparently successful; but I’m not an expert, and it may fail some criterion that I am not currently aware of. Certainly looks okay to me, though, and a version with added Tb2O3 exhibits the desired green fluorescence, with minimal visible color.
Paul Lewing, in Seattle, is working on a definitive book
about china paint for the American Ceramic Society, and it’s
just possible that I may get a tiny mention in it for
fluorescent and glow-in-the-dark china paint, which nobody
else seems to have bothered with, even in the ’60s. We’re
working on a particularly wicked example so he’ll have a
photo for the book if he wants one.
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Last modified: Fri Sep 2 13:50:58 EDT 2011