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Matt Katz

Member Since 17 Mar 2010
Offline Last Active Oct 07 2011 12:12 PM
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#5495 Lusters

Posted by Matt Katz on 05 March 2011 - 08:19 AM

Ok Everyone,
Nothing has gone overboard yet, but I see tensions brewing.
We would like to keep this forum neutral and scientific.
If you make a claim, please avoid opinions and supply data to back up your statements.
We are all relying on the expertise of each other to advance the discourse.


#5494 Underglaze Under Clear Glaze

Posted by Matt Katz on 05 March 2011 - 08:07 AM



pinholling normally occurs when a glaze is too think and or the clay body is releasing gas maybe try a longer hold on your kiln at the glazes maturation point. then for the cooling i would cool it slow.


not true, read my previous posts in this thread.


yes, i did. but are there not many reasons for why pinholing may occur?


there are a few, but gas escape is only possible in once fire, never in bisque ware.


#4003 Underglaze Under Clear Glaze

Posted by Matt Katz on 13 December 2010 - 08:05 AM

Pinholing is usually caused from gases escaping from the clay which did not burn off in the bisque. You could try bisque firing a little higher or slower or try soaking for an hour at the bisque cone temperature.
Marcia



We have done extensive study on that here at Alfred and that is a common myth. Because of the high viscosity of glass and the low pressure of gases, this is impossible. Pinholes are caused by poor packing of the glaze particles. If you want the background, you can check out Dave Finkelnburg's NCECA talk from 2007.


#3329 Correcting Porcelain Recipe

Posted by Matt Katz on 29 October 2010 - 08:20 AM

30% clay is not enough. It should be more in the range of 50%.


#966 Vitrified Stoneware Strength: Cone 10 Vs.cone 6

Posted by Matt Katz on 04 June 2010 - 11:39 AM

GIVEN:
- Stoneware A has a broad firing range, Cone 6 - 10
- Stoneware B has a narrow firing range, Cone 5 - 6

I take that to mean the following:
- A vitrifies fully at cone 10
- B vitrifies fully at cone 6


QUESTION:
Is A at cone 10 more vitrified (and stronger) than B at cone 6?
Or are they basically equal in terms of vitrification and strength?


Good question,
That really depends on the clays themselves. Many Cone 6 clays are not fully vitrified anyway. So you want to ask for their absorption and density numbers. a full vitrified body will have a density of between 2.35 and 2.45 (g/cm^3) and an absorption of >0.5%, independent of temperature


#227 Crimes And Mythdemeanors

Posted by Matt Katz on 05 April 2010 - 11:54 AM

Hi All,
I wanted to welcome everyone to the Ceramic Arts Daily Forum.
My name is Matt Katz and I will be the moderator around here.
If anyone has any questions or concerns around here, please PM me.

I wanted to start my first topic with an open forum to discuss common myths that plague the ceramics world.
There is a litany of these things and I will add to them as we go. Please feel free to add your own or ask a question about something you have heard but are unfamiliar with. No question is too rudimentary, in fact I'm going to start with one that most of you may know, but some may not.

Air Bubbles in Clay DOES NOT cause work to explode.
Explosions in ware are always caused by Water/Moisture that remains in the clay.
As a kiln heats and work warms, any remaining water in the body is quickly converted to steam. The steam rushes to escape the ware. If the release of steam is faster then the steam can leave the body, pressure builds and then the clay pops like an over inflated balloon.

So dry your work thoroughly! To that end, avoid Hotboxs to dry. Hotboxes can cause similar failures and aid in cracking.
A fan will do a much better job...but that is a topic for another day.


#225 Leaching & Unsafe Glaze Surface

Posted by Matt Katz on 05 April 2010 - 11:40 AM

I was once told that if a glaze that should fire to a gloss finish has any amount of matt finish then it would not be suitable for food due to leaching? I would think this would also depend on the glaze ingredients. Can anyone add to this please


There is no corelation between Matte glazes and food saftey. A properly formed Matte Glaze is a gloss glaze that crystals form in upon cooling. This is a result of composition and an abundance of Alumina and Calcium (or other Alkaline Earths) in your glaze matrix. Because of this, a properly composed matte is food safe.
Improperly formulated mattes are under fired and can be non-food safe