David Hendley on thu 5 aug 99
At 02:09 PM 8/3/99 EDT, Evan wrote:
>----------------------------Original message----------------------------
>I'm curious. Is there a reason to use magnesium carbonate when you
>could substitute dolomite for that and part of the whiting?
No, there is no reason to use magnesium carbonate in this glaze
(below). By the time a glaze is melted, it doesn't matter where the
magnesium came from.
There are some special situations where the raw ingredient
selection can make a difference before the glaze is melted.
For example, magnesium carbonate might be used to promote
crawling in a litchen glaze because it shrinks a lot. Sometimes
wollastinite is used instead of whiting, so there will be less
'boiling off' of the carbonate that could cause pinholes.
And, of course, bentonite is used instead of kaolin in low-clay
glazes so the raw glaze will remain suspended and stay on the pot.
I have been a potter for 25 years and never bought any magnesium
carbonate until last year, when I wanted to try some litchen glazes.
Mag. carb. costs about $3 a pound from my supplier.
Dolomite is about 30 cents a pound, and talc is 12 cents a pound.
All three provide magnesium, so when I want magnesium in a
glaze, guess which material I choose?
Working at cone 10, the only glazes I use that require dolomite
instead of talc are some low-silica, high-alumina matt glazes.
None, except for the special-case litchen glaze, need magnesium
carbonmate.
I also have never bought any lithium carbonate, as spodumene
works just fine for 1/10th the cost. Nor, Cornwall Stone, because
domestic feldspars contain the same oxides. If I lived in England,
of course, I'd use Cornwall Stone; there's just no reason in my mind
to ship feldspar across the Atlantic.
If you are comfortable with glaze calculation, and with the advent
of computers, it's a quick and simple matter, when you see a recipe
you'd like to try, to make to make these substitutions. Many, many
potters, however, don't know this, so the old recipes that include
needlessly expensive ingredients live on.
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com
At 02:09 PM 8/3/99 EDT, you wrote:
>----------------------------Original message----------------------------
>I'm curious. Is there a reason to use magnesium carbonate when you
>could substitute dolomite for that and part of the whiting? I've seen
>this in other glazes and figured if I found one that I want to pursue, I
>would certainly test that, but in the mean-time, figured I'd ask.
>
>-- Evan in W. Richland who's off to take the dog for a walk and swim
>along the canal.
>
>douglas adams wrote:
>>
>> ----------------------------Original message----------------------------
>> I personally haven't tried this one but it is rated at cone 6 and should be
>> Translucent satin matt
>> Feldspar custer 48.5
>> Whiting 18.0
>> silica 18.5
>> kaolin epk 8.5
>> zinc ox. 2.5
>> mangnesium Carb. 3.0
>> Bentonite 1.0
>>
>> As wth my experience in using the faithful Mangnesium Carbonate, make only
>> enough glaze to get you through your project as it will settle in the
bottom
>> and become lumpy after a day or two. I use a transparent cone ^6 easy EASY
>> EAsy glaze on a white body that does well that you may want to try a test
>> tile. It will make raw umber shift a little if it has been bisqued onto the
>> pot.I have not used underglazes,yet, with it.
>>
>> Gerstley 50
>> Kaolin 17.5
>> Flint (silica) 32.5 Good interaction with clay body and nice
>> covering
>>
>> Good luck. Have fun! Douglas Adams
>>
>> At 05:02 PM 7/29/99 EDT, you wrote:
>> >----------------------------Original message----------------------------
>> >Hi.
>> >I am looking for a satin to matte transparent glaze that would work over
>> >Amaco underglazes (fired to cone 6-7). I have tested several recipes, but
>> >have not found one that works well. The most usual problems in my tests
are
>> >changes in underglaze color (blacks becoming bluish), underglaze running,
>> >and not enough translucency. Any ideas?
>> >
>> >Vivian Budnik
>> >
>
| |
|
