Earl Brunner on mon 8 oct 01
I wanted to comment on the mats that went glossy.
Mats come from two or three conditions, one it too much silica, so
silica remains in suspension in the glaze, another is too much kaolin,
or ball clay, and the other is from crystal formation in the cooling.
I would guess that your matt glaze/s might fall into the category of
either the first or second type, the added time at top temperature
allowed the silica or clay to enter fully into the melt. What you have
here is "heat work" as opposed to higher temperature affecting the total
melt, allowing things that previously might not have fully entered into
the melt to do so. In other words you achieve the similar result by
holding for a protracted period of time at one temperature that you
might by firing to a higher temperature for a shorter amount of time.
The dynamics are similar, but not exact.
And of course if someone else has a more accurate explanation, feel free
to jump in here.
Karen and Cliff Sandlin wrote:
> Here's what happened when I mistakenly programmed my 1018 Skutt to hold
> for 15 hours at Cone 5 temp of 2165 instead of 15 minutes as intended:
>
All
> the matt glazes are shiny now.
>
> The kiln itself appears to be fine.
>
> Karen
>
> ______________________________________________________________________________
> Send postings to clayart@lsv.ceramics.org
>
> You may look at the archives for the list or change your subscription
> settings from http://www.ceramics.org/clayart/
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@pclink.com.
--
Earl Brunner
http://coyote.accessnv.com/bruec/
bruec@anv.net
John Hesselberth on mon 8 oct 01
on 10/8/01 5:40 PM, Earl Brunner at bruec@ANV.NET wrote:
> I wanted to comment on the mats that went glossy.
> Mats come from two or three conditions, one it too much silica, so
> silica remains in suspension in the glaze, another is too much kaolin,
> or ball clay, and the other is from crystal formation in the cooling.
> I would guess that your matt glaze/s might fall into the category of
> either the first or second type, the added time at top temperature
> allowed the silica or clay to enter fully into the melt. What you have
> here is "heat work" as opposed to higher temperature affecting the total
> melt, allowing things that previously might not have fully entered into
> the melt to do so. In other words you achieve the similar result by
> holding for a protracted period of time at one temperature that you
> might by firing to a higher temperature for a shorter amount of time.
> The dynamics are similar, but not exact.
> And of course if someone else has a more accurate explanation, feel free
> to jump in here.
I think you are right Earl. It sounds like these glazes are normally matte
because they are not fully melted. Unfortunately a fair number of mattes
are made that way and, as a result, they are usually not at all stable or
durable. The only stable ones are the ones that get fully melted and then
crystallize out on cooling.
Regards,
John
Web site: http://www.frogpondpottery.com Email: john@frogpondpottery.com
"The life so short, the craft so long to learn." Chaucer's translation of
Hippocrates, 5th cent. B.C.
| |
|
