Ceramic Design Group on sun 3 apr 05
Seems to be some information and lots of misinformation going on the
list regarding glaze rheology. Taylor and Bell in "Ceramic Glaze
Technology" offer a good discussion. For most glaze work, if there is
sufficient clay in the glaze it will suspend fairly well.This is a
blanket generalization I know. But proper glaze suspension is only
part of glaze rheology. Not all glazes have sufficient clay, not all
glazes can be sprayed and there are lots of questions. Its fairly
simple in understanding the basics. I'll summarize what works for me,
in a general way. You will have to test your glazes and determine what
their proper rheology is for your use.
1. In order to glaze efficiently and have the glaze work the way it is
meant to, actually which means provide the results you want, you need
to know its specific gravity or weight, and its viscosity, or
resistance to flow. These are simple calculations even for those of us,
like myself, are quite math encumbered.
2. Every glaze needs to have materials to suspend it, to make it fluid,
to make the surface resistant to chipping and dusting, and to have
binders that keep all this together, happily.
3. Glazes for dipping have different weights than those for spraying.
4. CMC is a binder and works very well. There are also other binders
such as Peptapon and Optopix that work well. Some glazes don't require
binders. In some formulations, you can use V Gum Cer not only as a
glaze suspender but it can function also as a binder.
5. You can achieve good glaze poise and fluidity using a deffloculant
such as Darvan 811, one of the many chained polymers available from RT
Vanderbilt. My experience with sodium silicate is not to use it in
glazes. I also don't get near sodium silicate/soda ash deflocculation
systems for my casting slips. Stuff is nasty and rides a very narrow
edge.
6. Surface strengthening additives such as PVA are a great addition to
the glaze.
7. I like to keep it very simple and for me, its a combination of V Gum
Cer, PVA, and Darvan 811. I have glazes that are very high in frits,
low in clay, and the combination of these 3 ingredients provide a
really workable glaze slop for us. I have different specific gravities
for glazes that I spray, and those that I dip. Its wonderful to see a
glaze mixture spray on and lay down, so to speck, in a very dense
layer, resistant to handling and does not dust. I mix the V Gum into
hot water as an aqueous dispersion with a high sheer mixer. The I add
the 811 and PVA. After mixing, I add the dry glaze ingredients. Mix
sieve, keep mixing and sieving, and then check my numbers for SG and
viscosity.
9. If you keep records and check the specific gravity and viscosity of
your glaze before each glazing session chances are that your ware will
look remarkably better as the coating of glaze will have the correct
thickness and poise.
10. All this taken into consideration, you will have to find the
correct proportions of additives and the correct specific gravity and
viscosity for the glazes you use. But these guide lines work.
Jonathan
Jonathan Kaplan
Ceramic Design Group
PO Box 775112
Steamboat Springs CO 80477
(970) 879-9139
Plant location for commercial deliveries excluding USPS
1280 13th Street Suite K
Steamboat Springs CO 80487
info@ceramicdesigngroup.net
www.ceramicdesigngroup.net
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