Lee Taylor on thu 22 sep 11
Dear list-mates:
I have been raw glazing (or attempting to do so) for much of the last 20 =
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years=3D20
or so. There was a learning curve for me that became frustrating at firs=
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t.=3D20=3D20
However, the effort has paid off in the long run. I believe that many fo=
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rms=3D20
are not well suited to dip glazing when raw. The forms which can be=3D20
consistently successful with this type of glaze application must be struc=
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turally=3D20
sound and of uniform thickness (for the most part). Handles must be=3D20
substantial and well attached. I have not tried spraying glazes, though =
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I have=3D20
recently purchased a sprayer. Spraying should be much less technically=3D2=
0=3D
challanging, but probably more time consuming.=3D20=3D20
I find that the clay body used determines whether the glaze should be app=
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lied=3D20
when the pot is green or just past leather hard. The absorption rate of =
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the=3D20
clay is critical. Groggy/open bodies are way more absorbant and must be=3D=
20=3D
glazed when still damp (but no so much so that they collapse-or the handl=
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e=3D20
falls off) when the glaze is applied. Tight bodies (porcelain and fine s=
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toneware=3D20
are my experiences) can handle glazing green, though it is a little riski=
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er in my=3D20
opinion. Greenware soaks up more water than the leatherhard clay and the=
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=3D20
expansion rate and directions of expansion when rewetted become an issue.=
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=3D20=3D20
Any fault or weakness in the pot will be revealed when rewetted by an=3D20
irreparable crack. Leatherhard glazing is more forgiving overall. Dryin=
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g of=3D20
larger forms, after glazing, should be controlled to assure that the rims=
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and=3D20
handles don't dry our first (shrinking faster than the rest) causing crac=
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ks...just=3D20
like with any other pot.
I glaze large forms, like bowls, one side at a time, outside first, then =
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let dry to=3D20
leatherhard again so it can be handled easily, in order to avoid over-wet=
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ting=3D20
and collapse. Batter bowls, with heavy handles and a base smaller than t=
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he=3D20
rim, work well with a two step glaze application, as well. It sounds lik=
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e a lot=3D20
of trouble, but it really goes smoothly, once you get the timing figured =
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out.=3D20=3D20
You can slow down or speed up the drying times to fit your schedule. I h=
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ave=3D20
a 40 hour non-clay job and have no trouble making it work.
I have recently been given a small electric kiln, but would never conside=
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r going=3D20
back to bisque firing. I am a committed single firer! I believe that th=
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e=3D20
glazing/decoration is more directly a part of making and it is somehow mo=
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re=3D20
satisfying.
I have not found a glaze recipe that cannot be made to work with raw=3D20
application. The trick is to match the shrinkage upon drying between the=
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clay=3D20
body and the glaze, so that the glaze does not shrink less than the clay =
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and=3D20
just crack or peel off when the work is fully dried. My rule of thumb is=
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to add=3D20
8% of the total weight of dry ingredients of the glaze in bentonite. If =
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the=3D20
original recipe is largely clay, then I will back off on this number a l=
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ittle.=3D20=3D20
Though this figure is at the top end of what most sources recommend, it =
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has=3D20
worked well over the years for me. I am having a problem now with a high=
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=3D20
silica glaze that shrinks way less than the other glazes I have been usin=
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g. I=3D20
keep a bucket of bentonite slurry handy and just keep adding a little at =
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a time=3D20
until the glaze fits! I expect that I am now up to about 10% bentonite i=
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n this=3D20
particular glaze. One other factor to consider is that some clay bodies =
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shrink=3D20
more upon drying than others. However, I have had no trouble finding a=3D2=
0=3D
happy medium in bentonite content so that a particular glaze fits all of =
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my=3D20
clay bodies.
The firing is just like an extended bisque firing...go slow and NO reduct=
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ion until=3D20
after bisque temperature and all of the organic material has burned out, =
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then=3D20
continue as a normal glaze firing. I have heard that some glazes trap or=
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ganic=3D20
matter underneath. I have not had this happen yet.=3D20=3D20
Tichane, in his book on ash glazes, says that there is a more developed=3D2=
0=3D
interface between the glaze and clay body with raw glazing, which enhance=
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s=3D20
the depth of celadon and jun (high alkaline) glazes. He says that most o=
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f the=3D20
early Asian pots were raw glazed. Dennis Parks has an old book "Raw Glaz=
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ing=3D20
and Oil Firing" which is not a lot of help. Fran Tristram's book "Singl=
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e Firing" is=3D20
more helpful. But, just getting in there and doing it is the best way to=
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learn!
Overall, I think raw glazing is a great way to go!=3D20=3D20
Lee Taylor=3D20
Lexington, Virginia
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