Firing Results, starting 29 September, 2004

A Joss Research Institute Interim Report

(30 September, 2004)

I fired two glaze tests yesterday, one of which provided an odd and interesting result.

In the Spring, I reported on a found material, some apparent low-grade iron ore that occurs in the “panhandle” section of Maryland, and in southern Pennsylvania and New York. A few weeks ago, I managed to collect a sample from each of those two states. Here’s the Pennsylvania material, sitting out in front of #19:


I melted a material very similar to this (actually a Maryland sample) at cone 9 or so in the electric kiln, this past spring, and got the following:


In addition to the Maryland and Pennsylvania samples I got a sample of the equivalent rock from upstate New York, already weathered and crumbled. I ran some of it through the jar mill, and it fired out much like the example shown above, but perhaps a slightly richer color, so I’ve begun mixing it with fluxes to see what kinds of glazes I can get from it. Yesterday’s mix was 90% “NY State Red Rock”, 4% Whiting, 4% Magnesium Carbonate, and 2% Red Iron Oxide (84% purity). I fired it at about cone 8, in oxidation, expecting to get a somewhat dull semimatte black. So much for my intuition: it’s a lovely semigloss mid-gray (photo on the left; I’ve slightly overexposed the detail so you can see more of what’s going on in it) —


In the photo on the right I’ve applied a wash consisting of 3 parts Whiting and 1 part Silica. Where the glaze is thin, the wash entirely bleaches it; where the glaze is thicker, the wash turns it into a Tenmoku (so-called; this term actually refers to pottery styles, not to glazes) or something very much like one, with tiny yellow-green crystals of some sort around the edges of the dark spots; quite pleasant.

This is definitely a keeper. I’ve tentatively decided to call it “Trooper Teadust”, partly because it is nearly the color of a NY State Trooper’s uniform. (The trooper in question was extremely kind about letting me take samples at the roadside.)

(02 October, 2004)

Well, slap me silly: we are all taught to think of teadust as underfired tenmoku black, so I stuck a test tile of this glaze into the little gas kiln and gave it a bath at cone 9, in reduction, figuring I’d get a nice deep glossy transparent black. I was, uhh, wrong.


(Yes, that slanted line is cyanoacrylate glue — I dropped the damned test tile a few minutes after I got it out of the kiln. Argh.)

It looks like this one’s a keeper no matter how I slice it. Some days you just get lucky.

“Troopersimmon” Revisited

(09 October, 2004)

I fired a test of this glaze (to cone 10, in reduction) with a 1% more Red Iron Oxide and 1% more Whiting than was in the original, and was not happy with the result. It was rougher, more crystalline, and a bit darker, which to some extent obscured what the Red Iron Oxide wash did to it. I also didn’t think it was really as attractive.

I fired one today, again to cone 10r, with 1% more Whiting than the original, but 1% less iron. Here are photos of the test tile. (These are overexposed a little, which makes them look significantly more orangy and less brown than the test tile itself. The photos just above are closer to the real color, at least on my monitor.)


Here’s a detail of the side with the washes...

(If you want it even more close-up and personal, try this, but be aware that it’s over 800 kB.)

[The reddish crystals that you can see in a diagonal stripe in each photo are what I get with a wash of plain Red Iron Oxide in water; the yellow stripe is a wash of Rutile and Gerstley Borate; those were painted on with a brush. The dark-to-transparent regions are a wash of 3 parts Whiting to 1 part Silica, "schpritzed" on with a toothbrush from a short distance. Notice that the glaze itself is a little smoother, a little closer to glossy than the original was.]

I’m really pleased with this. It has a lovely texture, and very even color except where the washes do nifty things to it. Think my next step is to make a batch and try putting it on actual pieces, so I can learn how to use it effectively.

(11 October, 2004)

Here is a page about the "Red Tenmoku" bowl I fired (to cone 10r) yesterday.

I’ve been trying for this color for a very long time, and I’ve written a somewhat blathery page about it.

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Last modified: Tue May 9 11:30:55 EDT 2017