Mike Gordon on mon 12 mar 01
Hi,
Patience is running thin here. What temp and what atmosphere? Oxy or
red.?? Mike Gordon
Lili Krakowski on mon 12 mar 01
I hope Mel et al will forgive me for sending so many babbles or rants or
posts or messages--whatever--all at once. At last my hand is usable, at
last I can type, badly as always, and I need to dipatch some stuff
before I go off CLayart. As I do not yet have e-mail at home--maybe in
2002--I want to get this done. I truly hope that some of you good guys
will keep this info and repost it when relevant questions are asked.
I print out all relevant stuff and then hand out at workshops/classes
mail or etc.
Again:
All of you who are upset because Gerstley Borate which replaced
Colemanite weny off the market, get a grip. GB ideally contains 1 part
of calcium for 1.5 parts boron. That's all. It also shrinks a lot. It
also like ALL MINED PRODUCTS varied from mine run to mine run, source to
source. In Frits the proportion of boron to the other ingredients
matters, N ot that much, but it matters. Some frits HAVE boron but not
calcium but have Soda or Potash. Others have lots of calcium, less boron.
Some have alumina some don't.
My method has been to get a pound of each available ZINC FREE boron frit
(zinc free as I do not want to affect my slip colors) and try them all as
gram for gram equivalents in my GB glaze.
AND TO THAT POOR VICTIM OF A HOSTILE GLAZE: Why did you put a new glaze
on a POT? For every batch of a glaze no matter how trusted and adorabld,
fire a sample on a tile or shard, properly supported on a thin
biscuit/cookie/wafer of clay BEFORE REAL USE. Remember Lucie Rie said she
fired test tiles in all her glaze firings.
For you abroad: Ferro Frits are wellknown enough so hat you can go to a
Podmore or similar dealer and say: Yo. What you got comes closest to FF #
whatever.
MOPE E5-- A Hobart Cowles Glaze
Ball Clay 5
Frit 3134 50
Frit 3195 5
Whiting 20
Neph Sy 25
Silica 15 Zirconium opacifier 10
The MOPE series is very pretty. I expect this can be recalculated for
fewer ingredients. If I mixed this up ever again I would replace Ba;ll
Clay with Bentonite.
NADYA (A Hobart Cowles Glaze)
Ball Clay 9
Bentonite 13
Dolomite 13
Frit 3124 28
LITHIUM 3.5
Silica 30
I would omit the Lithium these days and use maybe a spoon of soda ash
instead. I would test first just plain without the lithium. Probably
will work, or, with all tha bentonite, would reduce/eliminate the ball
clay.
E4MSP "Cowles E4" (Hobart Cowles glaze)
Frit 3134 35-37 (higher needed for more refractory colorants)
Dolomite 12.5
Potash Spar 15
Clay 30
Flint 15
Tin 5
CaO .4585 Al2O3
Na2o .2522 .4817 SiO2 3.063
MgO .2245
K20 . 0648 B2O3
.4648
Lovely with 10% yellow stain
In 1984 or so Ceramics Monthly pulished Hobart Cowles's glazes in 4
issues. Check'em out.
AS WITH ALL TRANSCRIBED FROM BOOKS AND NOTEBOOK RECIPES: THE ORIGINALS
WORKED. ANY ERRORS IN TRANSMISSION ARE MINE.
WHAT IS NOT MINE IS THAT THE RAW MATERIALS VARY CERTAINLY OVER THE
DECADES..SO YOU MUST TEST. N O REPRESENTATION IS MADE AS TO SAFETY WITH
FOOD.
Lili
Krakowski
Tom Buck on tue 13 mar 01
David Hendley, others:
Plainsman Clays/Digitalfire Corp. (Tony Hansen is responsible) has
developed and NOW is marketing Boraq. It is a reconstrcution of Gerstley
Borate in its good days, using minerals from afar (Chile for one).
This material isn't cheap, 1 kilogram costs approx $2.50 US
(nearly $4 Cdn), and is available in Toronto and I believe Axner's will
stock it as well.
But it does emulate GB quite well, including the familiar
"gelling" in the bucket. One low-fire potter came up with a satin matt at
C05/04 using an adaption of the 1:2:3 recipe (by volume, 1 silica/flint; 2
kaolin; 3 Boraq). Another potter, high-fire reduction, was able to achieve
a motled blue alongside his copper red glaze, reproducing the same effect
that Gerstley Borate gave, and an effect not found with other GB
substitutes.
So, for Rakuers, others, Boraq offers hope that the traditional
GB glazes will be available again without any adjustment.
til later. Peace. Tom B.
Tom Buck ) tel: 905-389-2339
(westend Lake Ontario, province of Ontario, Canada).
mailing address: 373 East 43rd Street,
Hamilton ON L8T 3E1 Canada
David Hendley on tue 13 mar 01
Lili, there is more to the Gerstley Borate dilemma than simply
finding a frit as a suitable replacement. This will work fine
for a stoneware glaze with 5 or 10% Gerstley and plenty of
clay in the recipe.
It will not work for a raku glaze that is 50% Gerstley borate.
Frits are ground glass, and you will end up with a hard chunk at
the bottom of your glaze bucket.
So no, it's not the end of the glaze world, but it is a problem
that has not been completely solved yet.
As for trying frits, it is much more accurate to substitute by
using glaze calculation than to simply try every frit. Just select
a frit that has an analysis similar to Gerstley, change your
glaze recipe to a formula, and calculate a new recipe using
the frit. At present, there is no frit that is a direct one-for-one
substitute for Gerstley borate. This may change if there is
enough demand.
The synthetic Gerstley Borate makers are attempting to
manufacture a material that approximates the chemical makeup,
as well as the raw handling properties, of G.B.
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----- Original Message -----
From: Lili Krakowski
To:
Sent: Monday, March 12, 2001 1:20 PM
Subject: more about glazes
|
| Again:
|
| All of you who are upset because Gerstley Borate which replaced
| Colemanite weny off the market, get a grip. GB ideally contains 1 part
| of calcium for 1.5 parts boron. That's all. It also shrinks a lot. It
| also like ALL MINED PRODUCTS varied from mine run to mine run, source to
| source. In Frits the proportion of boron to the other ingredients
| matters, N ot that much, but it matters. Some frits HAVE boron but not
| calcium but have Soda or Potash. Others have lots of calcium, less boron.
| Some have alumina some don't.
|
| My method has been to get a pound of each available ZINC FREE boron frit
| (zinc free as I do not want to affect my slip colors) and try them all as
| gram for gram equivalents in my GB glaze.
|
| |
|
