[Clayart] small mis-statement

paul gerhold gerholdclay at gmail.com
Fri Feb 26 00:12:15 UTC 2021


Vince.

I can agree with those definitions. I am going to run a test with all my glazes where one firing is all out and the other will slow approaching the cone. Of course some have already been tested since my replacing the elements has cut firing time almost in half with no obvious change in those glazes, 

Paul

Sent from my iPad

> On Feb 25, 2021, at 5:59 PM, vpitelka at dtccom.net wrote:
> 
> Hi Paul - 
> The term "matured glaze" can be defined two ways.  A mature glaze can be a personal choice, meaning that you are getting the exact glaze results that you want, even if that's not what many other people would want from the same glaze.  Or, a matured glaze might mean what people generally agree is the most beautiful and functional result achieved from a certain glaze.  There is a lot of leeway in matured glaze depending on personal tastes and the intended use of the ceramic product. 
> 
> So, "glaze maturation" refers to what happens in the firing as a glaze achieves its most desirable and functional qualities, and for a lot of the most desirable effects, that requires a slowdown approaching "maturation" temperature, and for many potters, controlled cooling.  
> - Vince
> 
> Vince Pitelka
> Professor Emeritus of Art/Ceramics
> Appalachian Center for Craft
> School of Art, Craft & Design
> Tennessee Tech University
> Now Residing Chapel Hill, NC
> vpitelka at dtccom.net
> www.vincepitelka.com 
> 
> -----Original Message-----
> From: Clayart <clayart-bounces at lists.clayartworld.com> On Behalf Of paul gerhold
> Sent: Thursday, February 25, 2021 8:48 AM
> To: Clayart international pottery discussion forum <clayart at lists.clayartworld.com>
> Subject: Re: [Clayart] small mis-statement
> 
> Actually I do know that cones bend at different final temperatures depending on rates of energy input. I am not aware I ever said anything different but since the cone is the accepted way of categorizing a glaze that is the measure of glaze classification I used in my posts. And I have never suggested that rate of firing does not affect crystal formation dependent glazes.
> 
> My question remains about what is the definition of a “ matured glaze” 
> 
> Paul 
> 
> Sent from my iPad
> 
>> On Feb 25, 2021, at 7:13 AM, Joseph Herbert <josephherbert827 at gmail.com> wrote:
>> 
>> In a previous string of posts, Paul Gerhold made a small 
>> mis-statement about cones, firing rates, and end temperatures. Not one 
>> of the glaze gurus here, but it is my understanding that cones are 
>> known to perform differently for different firing rates.  Orton has 
>> two end temperatures listed for cones depending on rate of temperature 
>> rise.  The end temperature for the faster firing rate is higher than 
>> that of the slower firing rate.
>> 
>> There must have been several (scores ?) of master's theses done at 
>> Alfred over the years about this topic.  It seems like an easy topic 
>> to assign and a nightmare to complete.  A transparent glaze should 
>> perform relatively consistently from the time it is fully melted until 
>> maturity.  (although there apparently can be a significant 
>> contribution to the look of the glaze from bubbles) Any 
>> opaque/crystalline matte glaze must be bedeviled by the energetics of 
>> crystal growth or particle solution.  If the matte comes from 
>> immaturity, there are then particles from the original slurry that are still entering solution for the entire time the firing lasts.
>> 
>> If I were imagining such a research project, I would want access to 
>> X-ray crystallographic equipment, petrological thin section equipment, 
>> and optical/electron microscopes.  Also, I don't think two years would 
>> be even close to enough time for a result (other than negative).
>> 
>> When I had access to that stuff, I wasn't interested in pottery.
>> 
>> Actually, when I have had occasion to grind into  the surface of an 
>> opaque glaze, I have been startled by the complexity of the mix of 
>> materials lurking under the surface.  Bubbles, apparently clear glass, 
>> glass with crystals - just from momentary observation.
>> 
>> Joe
>> 
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