More testing

There’s a glaze that has been used by sculpture people for a fleshy surface. Lately Drew Avakian at UF has been looking into it for his constructed pottery. I like the waxy look, an tried it with iron. at 5% iron, it has dramatic thin-to-thick changes from rust to creamy, showing dark slip and breaking a bit on texture. Still testing the cordovan color to see if I can reproduce it on a piece. I think the tin could be lowered and still get results. Tin is expen$ive. Without the tin (and zirconium opacifier in its place), the color doesn’t quite look the same, I suspect. The waxy look and mottling is accentuated by the tin, and the iron color might be subtly different. But I don’t think it has to be 10%. I’m going to drop to 8%, and maybe later see if I can go to 5. The original glaze name is about using rutile to tint the glaze, and counts on there being some chrome impurities in the rutile to pink up the high-tin glaze. If doesn’t show on the test tiles, but on small pieces, thick glaze over the green copper + chrome slip does turn kind of mottled burgundy. It would take at least 5% tin if you care about chrome-tin pinking like that. I want the nice iron browns, waxy surface, and mottling/breaking.

Flash-oPink test tiles

Test tiles for the Flash-o-Pink glaze base, w/tin, and increments of Clear Creek yellow iron.

Testing for treasure

Clean Creek Products is a company that markets materials reclaimed from coal mining. They’ve had a booth at NCECA to showcase their iron and manganese. There is a show coming up that features these materials, and I’ve been working with their iron and manganese to try to get something pretty in a glaze. On top of most non-lead majolica glazes, iron is just so very brown. Not amber-golden, not rich rust, but just brown. I rarely use brown in my majolica color palette, so I thought I’d take this as a nudge to do some fun slip work with paper stencils and look for glazes to go over that that are rust or golden.

circles are unity amounts of oxides for Meyers Clear 04 compared to grey bars of normal limits

UF has some clear glazes for 04 use – Deb’s Clear and (Ron) Meyers Clear. Both have issues. The Meyers Clear is the main one. If it gets thick, you get evil small craters that won’t heal, and just get worse if re-fired. I think it’s too viscous. The alumina is high, in addition to having boron. I’ve tested some similar formulas with lower alumina. The  raw Meyers is also very high in frit. In addition to cost, high-frit glazes have to be applied unusually thinly for a good result – hard for beginners to judge.

The recipe for the Meyers Clear:
Frit 3124     89.8
EPK            10.2  plus 2 Bentonite.

When I look at the glaze under a 30x little microscope (Radio Shack has some that are cheap – $9.00 last I bought one), the glaze is filled with trapped bubbles. The up side is that it doesn’t run or even move, but it also in unforgiving about being too thick, and it’s very easy to get it that way.

My new version with less alumina and a bit more KNaO, and a test even less Al. Results were counterintuitive. The Less Alumina version of M4 has MORE bubbles that causes milkiness thick. Hmmm. Difference in clay color may be from different batches of test tiles. Using up old stuff. Slip colors very similar. Somehow, the bucket labeled WHITE SLIP is coming out pale yellow. Need to re-mix. Out of touch w/studio during the school year. Nice to get back to daily contact. M4 bleeds the black slip ever so slightly when thick. Maybe I can live w/that. I know just enough about glaze materials to know I don’t know enough. The M4 version looks better than the original Meyers Clear to me, but it will take testing on real thiings to see how it works.

Unity formula info from Glazchem:
Meyers Clear original
KNaO  0.302   Al2O3  0.392    SiO2  2.826
MgO 0.005       B2O3  0.541
CaO  0.693

Alumina:Silica ratio is  1.00:7.21 Neutral:Acid ratio is    1.00:3.03 Alk:Neut:Acid ratio is 1.00:0.93:2.83

Expansion: 74.8 x 10e-7 per degree C Oxides causing abnormal expansion:   B2O3

Clear M4
KNaO  0.336 Al2O3  0.326    SiO2  2.786
CaO 0.658     B2O3  0.545
MgO  0.006

Alumina:Silica ratio is  1.00:8.55 Neutral:Acid ratio is    1.00:3.21 Alk:Neut:Acid ratio is 1.00:0.87:2.80

Expansion: 77.5 x 10e-7 per degree C Oxides causing abnormal expansion:   B2O3

M4 Less Alumina
KNaO  0.337   Al2O3  0.247    SiO2  2.507
MgO 0.005    B2O3  0.544
CaO  0.658

Alumina:Silica ratio is  1.00:10.14 Neutral:Acid ratio is    1.00:3.18 Alk:Neut:Acid ratio is 1.00:0.79:2.51

Expansion: 80.5 x 10e-7 per degree C Oxides causing abnormal expansion:   B2O3

Glaze tests M4

Left M4 less alumina version, Right M4 glaze test

Limit formula chart for Clear M4

Limits M4 less alumina

Limit chart from GlazChem of M4 Less Alumina test




Glaze tests

Greenware serving platter w/slip decoration.

Greenware serving platter w/slip decoration.

My test tiles yielded a few things I thought worth trying. There’s a show coming up that’s about using the recycled iron and/or manganese from Clean Creek Products. Normally, brown is not high on my color favorites list. On majolica glaze, iron is just… brown. So, I was looking for something richer. Amber? Rust? One of my test was a nice mottled

Fired work from Glaze Tech kiln

Fired work from Glaze Tech kiln

rust-to-cream and showed darker slips. I tried a few pieces and really enjoyed my Skutt Glaze Tech little kiln – big enough to fit a serving dish and some other things in a load, but small enough that I can fire it every day or 2 and see the results before I commit to more work.

As often happens, I think I liked it best in the greenware state. Happy enough with the glaze results, though, but the color and value ranges are more subdued with the golden iron glaze over all.

Slips on earthenware w/a semi-opaque glaze.



Hello world!

For some time I’ve been enjoying the blogs of other people and thinking I should set one up to share various things. Time is always the question, but summer is a good time for me to begin.

I’ve just gotten a new Skutt Glaze Tech test kiln, and have been working on some iron and manganese glaze tests, trying for something more than plain brown. Check back in a few days for some test tile scans.

Expect some changes in format as I learn to use WordPress. Dreamhost, my web host, provides a one-click install, and I’ve taken the plunge, but I’m clueless about WordPress and doing some tutorials.