Alyssa Ettinger on sat 28 apr 07
hoping there's an easy solution for this that i just don't know about...
i work in cone 6, porcelain. some of my work is glazed inside and out, and
some only clear on the inside. for the latter, i try to once fire (to save
$$ on electric) and i use commercial clear because it's far easier to get
on. the fact that it's gloopy, syrupy, makes application really smooth, no
brush marks, etc.
is there anything i could be adding to my own clear recipe that would give
me this kind of consistency and ease of application? (i could use a spray
gun, but i don't like how much glaze it wastes.)
ideas?
alyssa
www.alyssaettinger.com
Dave Finkelnburg on sun 29 apr 07
Dear Alyssa,
Yes, you can adjust the viscosity of your raw
glaze. It will take some testing, though.
It is interesting you should ask this question
right now. I have been planning some exercises for
those attending my glaze workshop next weekend. We
are going to test all the ways there are to adjust how
glaze raw materials suspend in water. You just need
to do some of the same sort of testing...or, come to
the workshop! :-)
The factors controlling how your glaze applies
are glaze density, surface area of the glaze
particles, pH, positive ion (cation) concentration and
surface chemistry modifiers.
Density is easy to measure. It's just the weight
of any amount of glaze divided by the volume weighed.
The denser a glaze, the more it will tend to stay
suspended.
Total surface area of glaze particles is controlled
by the fine particles in the glaze. The coarse
materials have insignificant surface area compared to
bentonites and other clays.
Glaze pH can be adjusted with an acid or base. Low
pH flocculates clay systems, high pH does the
opposite.
Positive ions deflocculate a clay suspension in
water.
Surface chemistry modifiers are organic (like CMC,
or MAGMA, discussed below) and attach to particles
about like soap attaches to dirt.
These five factors work independently, but they can
be applied in combination, say by adjusting surface
area and density at the same time. The goal is to get
the combination that provides the glaze application
properties you want.
When you praise the application qualities of your
commercial glaze, by the way, you do need to keep in
mind that someone has been paid to make that glaze
work that way. A lot of experience and training in
surface chemistry has been applied to your glaze over
the years so it works for you. To match those
qualities you need to do some organized testing,
keeping clear notes, with your clear glaze.
MAGMA (Miracle Anti-Gravity Multipurpose Additive)
is a new product out which is distributed by David
Pier. He claims it will do everything you want. It's
expensive (~$20US/lb) but David says you only need 0.4
to 0.1% in a glaze. It's an organic, so it also
hardens a glaze. It slows glaze drying, and raises
viscosity, but if you add too much, your glaze takes a
loooooong time to dry! I'm sure you can find it from
many suppliers but I heard about this material from
Cindy Bracker at Bracker's in Lawrence, KS, where Pete
Pinnell is teaching a glaze workshop, also next
weekend.
For those who may have an opportunity to attend my
workshop May 5, 6 there's room. See details at
http://www.revivaltileworks.com/revivalworkshops07.html
Good glazing,
Dave Finkelnburg
Date: Sat, 28 Apr 2007 23:08:04 -0500
From: Alyssa Ettinger
i work in cone 6, porcelain. some of my work is glazed
inside and out, and
some only clear on the inside. for the latter, i try
to once fire (to save
$$ on electric) and i use commercial clear because
it's far easier to get
on. the fact that it's gloopy, syrupy, makes
application really smooth, no
brush marks, etc.
is there anything i could be adding to my own clear
recipe that would give
me this kind of consistency and ease of application?
(i could use a spray
gun, but i don't like how much glaze it wastes.)
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