[Clayart] glaze pops

[Edouard Bastarache]

Blisters Ampoules Blazoj

http://ampoloj.blogspot.ca/

Edouard Bastarache

----- Original Message ----- 
From: "Pfeiffer Fire Arts" <firearts at ardmore.net>
To: "'Clayart international pottery discussion forum'" 
<clayart at lists.clayartworld.com>
Sent: Tuesday, May 08, 2018 9:53 AM
Subject: Re: [Clayart] glaze pops


Glaze pops is what they look like but should be called blisters and pin 
holes. Looks like a bubble that pops and does not heal. We have been moving 
into a new batch of clay over the last year and it could in part be a clay 
problem but we do not see the same thing on our copper red firing. As the 
red is very fluid and our ox base is very stiff we then to think it a glaze 
problem.
We don't use plaster so that should not be the problem.

The clay does have a lot of grog in it and most of the problems do seem to 
be in the trimmed part of the ware but not always. I do take care to go over 
the trim parts with thawing slip to remove scratches and get a smooth 
surface.

We have been thinking of changing clay but that is always a big deal and I 
am not sure what to replace the current one with.
We are using a white ovenware ^10 clay (high-water phoenix ). Any other 
suggestion on a good ovenware clay?

Dan & Laurel

-----Original Message-----
From: Clayart [mailto:clayart-bounces at lists.clayartworld.com] On Behalf Of 
Vince Pitelka
Sent: Monday, May 07, 2018 8:56 PM
To: 'Clayart international pottery discussion forum'
Subject: Re: [Clayart] glaze pops

Hi Dan -
Can you be more clear about what you are referring to as glaze pops?  I am 
familiar with lime pops, which are usually the fault of the claybody 
(limestone contamination) or plaster contamination.  I am not familiar with 
"glaze pops."
- Vince

Vince Pitelka
Appalachian Center for Craft
Tennessee Tech University
vpitelka at dtccom.net
sites.tntech.edu/wpitelka/

On Mon, May 7, 2018 at 1:03 PM, Pfeiffer Fire Arts <firearts at ardmore.net>
wrote:

> All,
>
>
> After a number of years of not having a lot of problems with pop's in
> the glaze it has got so bad as to put us out of business. I have been
> making small changes in our glaze to reduce the surface tension hoping
> this would help. It has not and the last firing was the worst of the
> lot. I am not sure there are 5 pieces that we can sell.
> This firing had a slow rise from 1700 to 1900 and then a hour dwell at
> the top to cone 10 - 11. When slow about 2000 to give things time to
> heel. If anything the pops are bigger with our new glaze then the old one.
>
> Our first glaze base glaze is:
>
> Epk                     12
> Petalite                14
> Wollastonite    20
> Silca             20
> Custer          33
> Bentonite               1
>
> Our most recent attempt is to add a frit:
>
> Epk                     6
> Cal Epk         6
> Petalite                15
> Wollastonite    17
> Silca             20
> Custer          29
> Bentonite               .5
> Ferro 3134              6
> Veegum          .5
>
> While the calculated CEO is very close (8.60 and 8.61) to the same for
> both versions we had some shivering when it was thick on one piece.
> Anyone want to guess what to do next.
>
> Dan
> PfeifferFirearts.com
>
>
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