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Matt Katz

Member Since 17 Mar 2010
Offline Last Active Oct 07 2011 12:12 PM

Posts I've Made

In Topic: Foodsafe stains?

20 September 2011 - 08:34 AM

The only way to know for sure is to have a laboratory test for leeching. Make a cup, glaze and fire it, then send it to a laboratory that can test for cobal leeching. Two frequently cited laboratories in the U.S. are: Alfred Analytical Laboratory, 4964 kenyon Road, Alfred Station, NY, 14803 and Brandywine Science Center, Inc., 204 Line Road, Kennett Square, PA, 19348. Call them and ask about how to submit, costs, etc.

Alfred Analytical is closed.

In Topic: Substituting feldspar

15 September 2011 - 08:14 AM

I have a glaze recipe I haven't used in about 40 years. It contains 52% feldspar and the firing temperature given is 1250. My current kiln only fires to 1000 so can I substitute borax for the feldspar to lower the ffiring temperature? Thanks for any help you can give me.

No, The substitution is more complicated than that. I would have to say that you need to look for a new batch of formulas. Your old formula is basically ^6 and you kiln is fining under ^04.

In Topic: Ceramic Ball

06 July 2011 - 08:07 AM

wire stilts is your best bet

In Topic: Keeping Glaze Suspended

23 May 2011 - 10:52 AM

I mixed up a small test batch of a the Chinese crackle glaze I found a recipe for in another topic.
As follows:
83 Custer feldspar
8 silica
9 whiting
Add 10 Zircopax

However, this glaze won't stay in suspension very long - starting to settle almost before I can get the lid off and start applying.
Anything I can do to help matters?

Glazes require 5-10% clay for suspension.

That would alter your formula substantially.
try 1-2 % bentonite as an alternative.

In Topic: Glaze And Glass?

02 May 2011 - 08:08 AM

This is a very loose explanation.A good glaze will be made of part glass, part clay and part flux.
The ratio between the glass and the clay determine the surface characteristic. The ratio between the flux and the clay determine melting temperature of the batch.
Glass is actually a liquid.."without an ordered structure" <- definition as described in Physics... and even as window panes, it is a very slow flowing liquid.


Marcia I learned something new a couple of weeks ago, I went to a lecture on glass as part of the Kansas State University open house, the professor giving it said glass is technically a liquid but it never flows. He said it was an old wives tail that old window panes got thicker at the bottom, the process of making glass in the past would leave one side thicker than the others and they would install that side at the bottom for more strength. He said he believed the old wives tale until he started studying glass, he does the glass blowing for the university from extremely fine tube to huge Frankenstein glass assemblages. Denice

This is correct.
Glass exists in a state called a "Super Cooled Liquid" meaning that it is still in liquid form, but does not flow at room temperature. For glass to flow in the idea of the old wives tale, they would need either substantial heat or geologic time.

As to the previous question and to clarify Marcia, Glaze is glass, they are one in the same. The major differences is that A) Raw glaze is in the material state having never been melted and is generally composed of Flux (feldspar and Carbonate) Flint (silica) and Clay. The glass that she is referring to is not true unless the formula contains a frit, which is a glaze that has been fully melted and ground into a powder. B ) We add Alumina for stiffness which most traditional glasses excludes because they want to have their molten glass to have a lower viscosity (Flow more) where as if our glazes flowed in the molten state, they would run right off the piece.