Gregory D Lamont on wed 16 feb 00
Greetings all,
A colleague of mine has been using the following glaze for years, but has
recently begun having crawling problems to the extent that she has had to
stop using the glaze. After trying various fixes to no avail, she's
stumped and I can't see which of the materials might be causing the
problem. I thought I'd put it out to you all for your analysis and
suggestions.
Seacrest Blue C/10R
54 Custer feldspar
13 Whiting
6 EPK
22 Silica
2.5 Zinc oxide
2.5 Barium carbonate
--------
100
Add:
1 Red iron oxide
1 Rutile
0.5 Cobalt carbonate
Thanks for your help.
Greg
E-mail address:
gdlamont@isunet.net
Pottery Web Page:
http://www.ourwebpage.net/greglamont/
Mailing address and Phone:
Greg Lamont
3011 Northwood Drive
Ames, IA 50010-4750
(515) 233-3442
Paul Taylor on thu 17 feb 00
Dear Greg
If your colleague has been using this glaze for years There is not
much wrong with the recipe even though Zinc has a bad reputation for
crawling. Any opalescent glaze has a tendency to crawl. That is why
industry prefers to use thin clear glazes over slips or on glaze enamels.
Obviously the glaze is worth keeping if the zinc etc gives the glaze a
special look. If it does not and it is only a muddy blue any old recipe will
do ( I wish we could do photies).
However if your glaze is glorious you have to work out what changed.
First suspect the water content of your glaze materials changing the
recipe.
Then the analyses of those materials and that is a real hard one to find
out. And in my experience unless they have changed source impossible to find
out.
The particle size of the materials may have changed. The smaller the
particles the more the shrinkage the more imperceivable little lines in the
glaze waiting to be fired.
Then the Ph of the glaze slop although the clay content is not high. A
flocculated glaze holds more water and shrinks more. Unseen Little cracks
appear especially on any lines or rims on the pot or ware a handle or lug
meets.
Then biscuit fired a little higher the glaze not gluing well to the pot.
A dolled up transvestite touching the pots with make up still on his
hands.
lastly. Dust. especially carbon dust(soot) from a stove.
Regards Paul T
ps personal replies to tamblin@go.com as well as ANU. People have been
having trouble with the latter.
----------
----------
>From: Gregory D Lamont
>To: CLAYART@LSV.UKY.EDU
>Subject: Help with a crawling glaze
>Date: Thu, Feb 17, 2000, 12:54 am
>
>
>----------------------------Original message----------------------------
>Greetings all,
>
>A colleague of mine has been using the following glaze for years, but has
>recently begun having crawling problems to the extent that she has had to
>stop using the glaze. After trying various fixes to no avail, she's
>stumped and I can't see which of the materials might be causing the
>problem. I thought I'd put it out to you all for your analysis and
>suggestions.
>
>Seacrest Blue C/10R
>
>54 Custer feldspar
>13 Whiting
>6 EPK
>22 Silica
>2.5 Zinc oxide
>2.5 Barium carbonate
>--------
>100
>
>Add:
>1 Red iron oxide
>1 Rutile
>0.5 Cobalt carbonate
>
>Thanks for your help.
>Greg
>
>E-mail address:
>gdlamont@isunet.net
>
>Pottery Web Page:
>http://www.ourwebpage.net/greglamont/
>
>Mailing address and Phone:
>Greg Lamont
>3011 Northwood Drive
>Ames, IA 50010-4750
>(515) 233-3442
Ron Roy on thu 17 feb 00
Hi Greg,
Here is the same glaze using different materials - it should cure the
crawling - if it does let us know. I left out the ZnO - no point in adding
it to a reduction glaze. If your colleague doubts that it's a simple matter
of trying the original without it - It just might be what is causing the
crawling. Getting more clay in a recipe usually helps the problem as well -
especially if it's a "tougher" clay.
There is lots of silica and alumina in this glaze so I suspect it will hold
that barium in OK - It would be a simple matter to replace it with CaO or
SrO if that is a concern.
Custer - 57.0
Wolastonite - 18.5
Barium Carb - 2.5
Old Mine #4 - 9.00
Silica - 13.0
Total - 100.0
RR
>----------------------------Original message----------------------------
>A colleague of mine has been using the following glaze for years, but has
>recently begun having crawling problems to the extent that she has had to
>stop using the glaze. After trying various fixes to no avail, she's
>stumped and I can't see which of the materials might be causing the
>problem. I thought I'd put it out to you all for your analysis and
>suggestions.
>
>Seacrest Blue C/10R
>
>54 Custer feldspar
>13 Whiting
>6 EPK
>22 Silica
>2.5 Zinc oxide
>2.5 Barium carbonate
>--------
>100
>
>Add:
>1 Red iron oxide
>1 Rutile
>0.5 Cobalt carbonate
>
>Thanks for your help.
>Greg
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
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