PTM on a pot!
Potash Feldspar 41
Ball Clay 13
Bone Ash 13
Red Iron Oxide 10
+ Dolomite 11
+ Lithium Carbonate 2
The glaze I know as PTM had its beginnings in a Mike Bailey and David Hewitt recipe that appears in the book, "Clay and Glazes" (edited by Emmanuel Cooper and Eileen Lewenstein). My potter friend, Peter W. had experimented with it a few years back. Peter rounded up all the numbers in the recipe, and accidentally added some dolomite to his test. The result was very promising, and better than the original, so he did a series of tests with increasing amounts of dolomite. I always loved the look of the glaze tests that he did, and borrowed Peter's recipe and tried to replicate Peter's results. My tests looked, OK, the glaze was very nice, but were missing something, and I started to suspect that an addition of Lithium Carbonate might help. A visit to Peter W. confirmed that the original recipe should have had Lithium Carbonate in it. A further batch of glaze was made up, and the tests with added Dolomite and Lithium look very nice indeed.
Close up of PTM with a little brushed on swirl of dolomite and water that provides extra fluxing.
What I like about PTM, is it is a little "wild". It moves and changes colour as it goes from thick to thin. Throwing rings show up well, and close to, or under magnification, the colour is very complex, showing flashes of plum, tomato, blue, orange, and brown.
I also tested Bailey's Red, that I found in John Britt's excellent book, " The Complete Guide to High-Fire Glazes". Only just now, as I am writing this, do I realise how closely the recipe resembles PTM. The result is quite different though, both in colour and in character.
Bailey's Red fired at cone 9.
Custer Feldpar 47 (I used potash feldspar)
Kaolin 13 (I used ball clay to help lower the maturing temperature)
Bone Ash 14
Lithium Carbonate 2.5
Red Iron Oxide 8
Close up of Bailey's Red.
Bailey's Red is a lovely glaze, the gloss is even, the colour even too. It is quite interesting up close, being made up of green and red flecks, a bit like looking at a pointillist painting done in two colours. I can see that the red would develop better if the glaze were thicker. The other thing that would almost certainly improve Bailey's (and probably PTM) would be a temperature soak at about 950 degrees Centigrade (1742 F) as the kiln is cooling. This would give a chance for some of the iron to re-oxidise. In the case of Bailey's this would result in less green flecks and more red.
Whilst I think about it.....
Some Recommended Reading.
I have recently been reading all sorts of useful things about the use of iron in glazes, and, for those wanting more understanding of such things, I recommend a look at this article from cone 6 pots iron glazes and achieving red.
Other experiments in this firing were with tenmoku glazes.
Dud mugs make great glaze testers.
One was a Black Tenmoku that I have used when firing to cone 11 or 12 in my wood fired kiln, but have not done much with at a humble cone 9 in the electric kiln.
China Clay 10, (I used Ball Clay)
Potash Feldspar 55, (I used Nephaline Syenite)
and red iron oxide 8.
Substituting Nephaline Syenite for the Potash Feldspar and Ball Clay for the China Clay should drop the maturing temperature a little, and this is what I tried.
BTM with red iron oxide.
At cone 9 the modified glaze had a satin gloss, that actually was rather nice, but it did not develop its full black and really wanted some more heat to do so, or needs a further adjustment of the recipe. I also tested this glaze with iron sulphate in place of iron oxide. Iron sulphate has the lovely name, crocus martis, and I wanted to compare it side by side with iron oxide in a glaze and see if I could detect a difference.
BTM with crocus martis.
There is one, and it is very subtle, and I find myself preferring the glaze that contains crocus martis, there is just a hint more warmth, and the beginnings of a red/brown change of colour where the glaze is really thin. I also tried the glaze with half the amount of iron, 4 percent, to see what colour that would give, and was rewarded by a yellow-green brown.
I also fired something that a recipe Peter W. had as Red Tenmoku.
Not really sure why it gets the name "red" as the glaze is a very dark brown to black usually. This matured very well at cone 9, and is a very presentable dark brown glaze with a slight reddish "break" at the rim of a mug where the glaze is thin.
Potash Feldspar 50
China Clay 10
Red Iron Oxide 8
Both the black and the red tenmoku glazes are good candidates for use as an under-glaze when doing chun type glazes.
Tenmoku, Temmoku, there are various spellings for this glaze. As to the meaning of the word, "the eye of heaven" is the meaning that I have heard most often, but I will leave you with a link to a site that has several more explanations of the word... Tenmoku meanings.
Errata..... I tried to post a little video on this, but had to take it off again as the sound got messed up "somewhere in the cloud"!