Nikom Chimnok on tue 7 dec 99
Hello,
Of late we've been working on a glaze composed mainly of beer
bottles, wood ash, and local clay. The colors are great, and for reasons
unknown to me it likes to grow crystals, which we like, but it is too
glossy. How might I try to dull it down a bit, while retaining the
characteristics we like?
Sorry I can't give much information about the Seger formula. The ash
is the problem--a constantly varying mixture of broken boards from torn-down
buildings, furniture factory waste, eucalyptus, rubberwood, mango, cashew,
and several other trees I don't even know the names of in English. For what
it's worth, Louis Katz once ballparked the alumina: silica ratio at about
1:15, tho his numbers were pretty generic. It's runny. I've added local
kaolin till it stopped running, but it wasn't pretty anymore.
What I'm too dense to deduct is the difference between a glossy and
semi-gloss or satin glaze. What is it?
TIA,
Nikom
Paul Taylor on wed 8 dec 99
Dear Nikom
Unfortunately the caricaturistics you like depend on a glaze that
is not viscose. As soon as you add more alumina you loose the crystals. If
you fire lower or add silica you may not form the nuclei that build your
crystals but it is worth a try .
Most other forms of matting agents like titanium are strong crystal
formers themselves and will make radicle changes to the glaze .
You could try either slowing the cooling of the kiln, or holding the
temperature of the cooling kiln at the temperature your crystals are
forming; thus creating a lot more crystallization and a mat serface. A
little tin may do the same.
Another idea is to spray a thin layer of another glaze or silica on
the top of the glaze but a more viscose glaze on top will probably crawl. A
layer of the mystery ash thinly sprayed may help.
I would really like to know how you get on. If you solve it -a
stable
semi matt glaze with crystals. You will have really done the biz.
I think all our glaze descriptions need to be standardized to run the
perfect world.
I have never met any body who was qualified enough to make clear
definitions except of course myself, before I gave up the drink. However we
can all do better than mutton fat or -for the vegetarians -butterfat. Could
we start to describe our glazes like those nobs who talk about wine. I am
sure it would be good marketing. Fine glossy opalescent green with a
smattering of diamond mist resting on the eye .
Paul
This is Ireland it's lashing rain.
----------
>From: Nikom Chimnok
>To: CLAYART@LSV.UKY.EDU
>Subject: Dulling a glossy glaze: How?
>Date: Tue, Dec 7, 1999, 2:16 pm
>----------------------------Original message----------------------------
>Hello,
>
> Of late we've been working on a glaze composed mainly of beer
>bottles, wood ash, and local clay. The colors are great, and for reasons
>unknown to me it likes to grow crystals, which we like, but it is too
>glossy. How might I try to dull it down a bit, while retaining the
>characteristics we like?
>
> Sorry I can't give much information about the Seger formula. The ash
>is the problem--a constantly varying mixture of broken boards from torn-down
>buildings, furniture factory waste, eucalyptus, rubberwood, mango, cashew,
>and several other trees I don't even know the names of in English. For what
>it's worth, Louis Katz once ballparked the alumina: silica ratio at about
>1:15, tho his numbers were pretty generic. It's runny. I've added local
>kaolin till it stopped running, but it wasn't pretty anymore.
>
> What I'm too dense to deduct is the difference between a glossy and
>semi-gloss or satin glaze. What is it?
>
>TIA,
>Nikom
Jim Bozeman on wed 8 dec 99
Try adding some magnesium carb to the formula.
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Michael Banks on wed 8 dec 99
Nikom Chimnok wrote:
> Of late we've been working on a glaze composed mainly of beer
> bottles, wood ash, and local clay. The colors are great, and for reasons
> unknown to me it likes to grow crystals, which we like, but it is too
> glossy. How might I try to dull it down a bit, while retaining the
> characteristics we like?
Not easily in my opinion Nikom. Two problems:
1.The the colour transmission of the glaze is intimately related to related
to the glossy surface. Matting it to any extent increases back-scattering of
light, reducing transmission colour intensity. Compare the colours of
frosted glass to high gloss glasses.
2. Common matting oxides such as alumina, CaO, MgO, TiO2, ZnO, BaO etc,
affect colour in a BIG way.
You might try sandblasting! or Adding silica progressively until the surface
turns frosty. Wiping with glass etching creme? But if you use extra oxides,
try barium as it matts glazes at highish concentrations and has a similar
colour response to the alkalis already present in the ash. Another
possibility is adding petalite until the glaze loses it's gloss, the lithium
in this also affects colour similar to the alkalis in ash.
Nikom also wrote:
> What I'm too dense to deduct is the difference between a glossy
and
> semi-gloss or satin glaze. What is it?
Microscopic roughness is the difference. Hi-gloss is smooth and flat and
light traversing it transmits in parallel unscattered beams. A
cross-section of the surface of matt glazes look like the teeth of a saw.
This jagged surface transmits light at all angles, scattering it upward and
downward back into the glaze (back-scattering).
Under-mature (underfired or underfluxed) glazes are matt due to the
undissolved mineral constituents being the surface of the glaze, instead of
glass. Other mature glazes are matt due to certain fluxes which promote
precipitation of microcrystals on cooling, -the sharp points of the crystals
disrupt the gloss surface by poking proud of it. This second class of matur
e true matt glazes are classified in regard to the flux responsible; lime
matts, magnesia matts, barium matts etc.
Good testing!
Michael Banks,
in NZ
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