Michael Banks on tue 28 dec 99
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Jan,
You don't mention whether your glaze has titanium. This is the best crystal
enhancer and can be used up to 10=25 or more, if your glaze can take it.
Larger amounts dull colour and reduce the gloss. Other crystal enhancers
include the oxides of vanadium, molybdenum and tungsten.
Another way to increase crystal size is to reduce the viscosity and surface
tension by decreasing the alumina further and replacing it with more alkali
frit. But the alumina/silica ratios you quote are way up there already and
short of pumping in soda ash this may not be an option as the glaze must
already be borderline stable. If you are into making your own frit,
potash-based frits have lower viscosity's than soda ones.
Your best option overall though, is to add titanium dioxide if you're not
already using it. One author states that 0.5 inch crystals (without
titanium) can be grown to over 5 inches (with titanium).
Michael Banks,
Nelson,
New Zealand
----------------------------Original message----------------------------
=3EAs I am dealing with crystal glazes for some years, with quite some
success, I
=3Ehave anyhow, a problem that till today
=3Ei am not able to solve in a satisfactory way.
=3EI have usually crystals size between 0,5 and 5 cm ( 1/4 to 2 '' ).
=3EOn a exhibition in Gent ( Belgium Europe) there where pots with huge
crystals
=3Esize 3-5'', some even on vertical surfaces.
=3EAs I am using my own fritte giving in general a glaze with a Al2O3 =3B =
SiO2
=3ERATIO 1: 131 to 1:152
=3ESome glazes are made with Ferro fritte 3110 giving a ratio 1:112 to
1:123
=3EFor some glaze I use a dolomite reception glaze at the bottom of the
object.
=3EThe firing cycles, depending from the type of glaze, is 1240=B0 to =
1265=B0
soaking
=3E30' at max temp. and 3-5 hours at 1160=B0-1150=B0
=3EIs there someone with this experience, do I need to change the soaking
range,
=3Eor is it a question of glaze composition?
=3EThanks for your advice,
=3EJan
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