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ash glazes/was flashing and cooling in wood-fired kilns

updated wed 20 feb 02


Mark Mondloch on tue 19 feb 02

Thanks Ruth, that was very interesting.

I've been playing around with making an ash glaze from my scrap glaze since
I sponge off quite a bit of glaze with the glazing methods I use and
generate allot of scrap- and can't throw anything away you know. ;) I've
been using 1 part ash, 1 part scrap glaze (I just think of the glaze scrap
as feldspar since most of my other glazes are primarily spar),and 1 part
redart clay. Interesting matt, surprisingly close to your #16 and #21 tiles.
If I add 10% silica it gets smooth and glassy which also seems to match your
tile results.

Mark & Sylvia Mondloch
Silver Creek Pottery & Forge
W6725 Hwy 144
Random Lake ,Wi 53075
----- Original Message -----
From: "Ruth Ballou"
Sent: Tuesday, February 19, 2002 9:19 AM
Subject: Re: Flashing and cooling in wood-fired kilns

> Ash effect lovers,
> I've posted 3 scans of ash tests done on a biaxial grid at
0 T
> he lower right hand corner is a bit blown out, but I think the rest of the
> tile comes through okay. These tests show the result of varying alumina
> silica on a grid of 35 glazes with a set group of flux materials. More
> information on this method is available at < >. I
> use a 60/40 ratio of ash/spar for the flux corner (lower left corner).
> content increases to 50% as you move up the tile;silica increases to 60%
> you move to the right. I picked the 60/40 ratio based on a line blend of
> ash/spar. Interestingly, this happens to be the same ratio of calcium/spar
> for the .9 CaO grid from Ian's first book, Stoneware Glazes. Since a lot
> ash is predominately CaO, I don't think this is an accident that I that I
> chose this ratio. I've learned that some of the Chinese lime historic
> glazes have been analyzed to have .9 CaO (according to Nigel Wood's book).
> I imagine that potters working with available materials have repeated
> experiments many times. For comparison, the single tiles are glaze 16 and
> 21 from the .9CaO set.
> All these recent posts about ash on pots sent me to look at my grid tiles
> again and compare them to a pot with a heavy hit of ash that was fired in
> train kiln.There on the pot are a range of the same glazes that appear in
> the high clay area of both grids (ash/spar and .9 CaO) These glazes are
> in silica and have moderate amount of alumina. Makes sense as the
> underlying clay body is contributing to the glaze.
> Guess I'll go look at my tiles some more and see what else I see and think
> about them some more.
> Ruth Ballou
> Silver Spring, MD
> Didn't get to sit down much during the firing. Forgot my chair. Stood next
> to the warm kiln instead. Unload tomorrow.