Corinne Null on wed 7 jan 98
Inspired by Jeff Zamek's article a few months ago about chemicals, I've
been going over my own archives of notes from clayart for the past 2-3
years, and also notes from a class by John Baymore on Ceramic Materials,
and have come up with few questions.
Why would anyone use:
Dolomite, when you can use magnesium and whiting?
Whiting, when you can use wollastonite and silica and magnesium?
Talc, when you can use magnesium and silica?
Rutile, when you can use RIO and titanium?
Am I way off base and missing something, or on the right track? Any help
will be appreciated!
Want to re-write the list, add to it, delete from it? Go for it!
Thanks,
Corinne Null
Bedford, NH
cnull@MCIONE.com
Linda Blossom on thu 8 jan 98
I'll just answer one of your chemical choice questions. Rutile. I use a
grade that is made for the paint industry, from US Pigment. It is very pure
and consistent. It costs less than titanium. I use it instead of titanium
in crystalline recipes.
Linda Blossom
2366 Slaterville Rd.
Ithaca, NY 14850
6075397912
www.artscape.com
blossom@lightlink.com
-----Original Message-----
From: Corinne Null
To: Multiple recipients of list CLAYART
Date: Wednesday, January 07, 1998 11:57 AM
Subject: Chemical choices
----------------------------Original message----------------------------
Inspired by Jeff Zamek's article a few months ago about chemicals, I've
been going over my own archives of notes from clayart for the past 2-3
years, and also notes from a class by John Baymore on Ceramic Materials,
and have come up with few questions.
Why would anyone use:
Dolomite, when you can use magnesium and whiting?
Whiting, when you can use wollastonite and silica and magnesium?
Talc, when you can use magnesium and silica?
Rutile, when you can use RIO and titanium?
Am I way off base and missing something, or on the right track? Any help
will be appreciated!
Want to re-write the list, add to it, delete from it? Go for it!
Thanks,
Corinne Null
Bedford, NH
cnull@MCIONE.com
Leslie Norton on thu 8 jan 98
Using the complex natural combinations like Dolomite, Whiting, Talc and so
on, usually create a "different" glaze because the chemicals are more
"intimately" associated, . It's similar to taking vitamin pills instead of
eating food with the same vitamins. I imagine if you took magnesium and
whiting and put them in a mixer for the next 5000 years you would get a
combination that worked exactly like dolomite.
Then again if you want to use magnesium and whiting instead of dolomite and
you like the difference, the do it.
Maybe there is a chemical engineer out there that may have a more sientific
explanation??
-Les
> -----Original Message-----
> From: Corinne Null [SMTP:cnull@mcione.com]
> Sent: Wednesday, January 07, 1998 8:57 AM
> To: Multiple recipients of list CLAYART
> Subject: Chemical choices
>
> ----------------------------Original message----------------------------
> Inspired by Jeff Zamek's article a few months ago about chemicals, I've
> been going over my own archives of notes from clayart for the past 2-3
> years, and also notes from a class by John Baymore on Ceramic Materials,
> and have come up with few questions.
>
> Why would anyone use:
>
> Dolomite, when you can use magnesium and whiting?
> Whiting, when you can use wollastonite and silica and magnesium?
> Talc, when you can use magnesium and silica?
> Rutile, when you can use RIO and titanium?
>
> Am I way off base and missing something, or on the right track? Any help
> will be appreciated!
> Want to re-write the list, add to it, delete from it? Go for it!
>
> Thanks,
>
>
> Corinne Null
> Bedford, NH
>
> cnull@MCIONE.com
Louis Katz on thu 8 jan 98
=3C/NOFILL=3E
------------------
Good Question,
Magnesium Carbonate causes crawling. Using Dolomite eliminates this
problem.
Chemicals in combinations usually melt easier as the different oxides
are in closer proximity. You could use alumina and silica instead of
clay in your glaze recipes, but you might have to fire much slower,
and your glaze might settle like a rock.
On the other hand most magnesium carbonate is relatively pure and you
know hwat you are getting. Dolomite and whiting vary more widely in
composition. Whiting is a genenric term. Some whiting is more like
dolomite than calcium carbonate.
Hope this helps with some of you Q's
Louis
David Hendley on thu 8 jan 98
I use what's cheap.
If that doesn't work, then I move up the price scale.
Magnesium carbonate, for instance, is a couple of dollars
a pound. Dolomite is 30 cents. Talc is 9 cents.
So....I reach for talc when the formula needs magnesium.
If the talc adds too much silica, I switch to dolomite, if the
dolomite adds too much calcium, I must use mag. carb.
In practice, formulating regular ^10 glazes, I almost never
get past the 'talc' stage and use very little dolomite and no
magnisum carbonate.
When you use 'minerals' you are using whatever was dug out of the
ground. That's why they are cheap,
When you use oxides and carbonates, you are using a refined product
that was more costly to manufacture.
The refined products are constant.
The unrefined will vary slightly from batch to batch,
so, in theory, you are giving up some accuracy when you use them.
David Hendley,
Maydelle, Texas
At 11:56 AM 1/7/98 EST, you wrote:
>----------------------------Original message----------------------------
>Inspired by Jeff Zamek's article a few months ago about chemicals, I've
>been going over my own archives of notes from clayart for the past 2-3
>years, and also notes from a class by John Baymore on Ceramic Materials,
>and have come up with few questions.
>
> Why would anyone use:
>
>Dolomite, when you can use magnesium and whiting?
>Whiting, when you can use wollastonite and silica and magnesium?
>Talc, when you can use magnesium and silica?
>Rutile, when you can use RIO and titanium?
>
>Am I way off base and missing something, or on the right track? Any help
>will be appreciated!
>Want to re-write the list, add to it, delete from it? Go for it!
>
>Thanks,
>
>
>Corinne Null
>Bedford, NH
>
>cnull@MCIONE.com
>
>
David Hendley
Maydelle, Texas
See David Hendley's Pottery Page at
http://www.sosis.com/hendley/david/
Tom Buck on thu 8 jan 98
Corinne : my take on your questions are:
1) Dolomite is CaCO3.MgCO3, a crystalline material with
equal-molar amounts of the two carbonates. It is tidier and cheaper to use
Dolo and not Magnesium Carbonate (a white fluffly powder that's a nuisance
to weigh out) combined with Whiting a purified form of limestone (CaCO3).
2) Whiting, made chiefly for the paint (coatings) industry, is
cheap and disperses readily, so it is preferred for high-calcium oxide
glazes (eg, alumina/calcia mattes). Whiting's major drawback is the CO2
that goes into the recipe with the CaO ... 44% of Whiting's weight goes
beyond the kiln as vapour. And unfortunately this weight-loss occurs at
high temperature (just under 900 C) appearing as gas bubbles in the
melting glaze. In many glazes, a lot of whiting means a soak at full
temperature is usually needed to heal burst bubbles. The use of
Wollastonite, although a more expensive material, avoids the off-gassing
and hence may prove to be a better choice. One would not require silica
and magnesium (presumably MgO is meant) if Wollastonite is used instead of
Whiting since Wollastonite is Calcium Silicate, CaO.SiO2.
3) Talc is magnesium silicate basic, with a simple formula of
Mg2Si4O10(OH)2 and the crystalline form likely combines MgO.SiO2 and
Mg(OH)2 and SiO2. The natural mineral has small amounts of other compounds
associated with it. If you need MgO in a glaze, talc is a lowcost source,
easy to use. Again, talc is better than MgCO3 and SiO2 as separate raw
materials unless the recipe calls for proportions that cannot be achieved
by the use of talc alone.
4) Rutile is cited as FeO.TiO2 but the rutile of commerce may be a
byproduct of producing high-purity TiO2 for the paint industry and other
industries, and it may have a different composition. Ceramic-grade rutile
is available in several levels of purity, so not all rutiles behave the
same way in a recipe. However, since rutile is used at amounts up to 6% in
a glaze recipe, small variations in rutile's purity should have a very
minor effect on the glaze. Since rutile always carries some iron oxide
with it, one would not require RIO+TiO2 as a substitute unless either the
RIO or the TiO2 were required in different amounts than those provided by
rutile. The advantage of rutile is low cost (vs TiO2) and being not
as messy to handle as RIO is.
Tom Buck ) tel: 905-389-2339 & snailmail: 373 East
43rd St. Hamilton ON L8T 3E1 Canada (westend Lake Ontario, province of
Ontario, Canada).
On Wed, 7 Jan 1998, Corinne Null wrote:
> ----------------------------Original message----------------------------
> Inspired by Jeff Zamek's article a few months ago about chemicals, I've
> been going over my own archives of notes from clayart for the past 2-3
> years, and also notes from a class by John Baymore on Ceramic Materials,
> and have come up with few questions.
>
> Why would anyone use:
>
> Dolomite, when you can use magnesium and whiting?
> Whiting, when you can use wollastonite and silica and magnesium?
> Talc, when you can use magnesium and silica?
> Rutile, when you can use RIO and titanium?
>
> Am I way off base and missing something, or on the right track? Any help
> will be appreciated!
> Want to re-write the list, add to it, delete from it? Go for it!
>
> Thanks,
>
>
> Corinne Null
> Bedford, NH
>
> cnull@MCIONE.com
>
shelford on sat 10 jan 98
One more point on this - if you need (for instance) magnesium and whiting,
why NOT use dolomite? Weighing out ingredients is tedious enough, why go
for 6 if you can get it for 3? I am pursuing, in idle moments, a kind of
holy grail of really simple and safe (but gorgeous, of course!) ^6 ox.
glazes, with no more than 3 or 4 ingredients. I would love to get to the
"pants pockets" measuring stage that mel talked about, but my gut feeling is
that ^10 reduction pulls more out of the materials to make a simple glaze
interesting at that temp. So far, my best ^6 ox. glazes usually have at
least 6 and usually 8 or more materials in them. So - back to the question
- if I can get two or three ingredients from one, of course I'll go for that
one. Minor variations between batches have never been more than very minor
in my experience - where I put it in the kiln usually has more effect.
The only caveat, of course, is when there is a real sea-change in the
quality of a material, like happened with colemanite.
- Veronica
>----------------------------Original message----------------------------
>Inspired by Jeff Zamek's article a few months ago about chemicals, I've
>been going over my own archives of notes from clayart for the past 2-3
>years, and also notes from a class by John Baymore on Ceramic Materials,
>and have come up with few questions.
>
> Why would anyone use:
>
>Dolomite, when you can use magnesium and whiting?
>Whiting, when you can use wollastonite and silica and magnesium?
>Talc, when you can use magnesium and silica?
>Rutile, when you can use RIO and titanium?
>
>Am I way off base and missing something, or on the right track? Any help
>will be appreciated!
>Want to re-write the list, add to it, delete from it? Go for it!
>
>Thanks,
>
>
>Corinne Null
>Bedford, NH
>
>cnull@MCIONE.com
>
>
___________________________________________
Veronica Shelford
e-mail: shelford@island.net
s-mail: P.O. Box 6-15
Thetis Island, BC V0R 2Y0
Tel: (250) 246-1509
Ron Roy on mon 12 jan 98
I was going to leave this alone but - while I do think cost of materials is
important - I think having stable glazes is the better strategy in the long
run.
Cutting down on the number of materials in a glaze will make weighing them
out less tedious but - you leave yourself open to losses due to variations
in many of the chemicals we rely on.
Even our feldspars go out of production - dividing the feldspathic content
of a glaze makes replacement much easier. I recommend having at least 5
materials in any glaze. If some of those materials are more variable than
others I recommend replacing some of that material with more stable ones.
Gerstley borate is a good case in point. If you have 20% in a glaze you are
asking for trouble - especially if that glaze is not balanced - in other
words relying on an over or under supply of some oxides for a special
effect. I recommend replacing some of that GB with a boron frit - more
expensive - but in the long run - less expensive.
Keep in mind the problems suppliers have - we tend to buy at the lowest
cost. This forces suppliers to sometimes change their supplier - to stay
competitive - If you are buying a bag of whiting every 2 years - what
happens if you are relying only on whiting in your glazes - instead of
sourcing CaO from dolomite, talc and wolastonite - and your supplier
decides they are going to save everyone some money and buy their talc from
a different supplier? The new whiting may not have the same analysis as the
old one. It is the same with other materials as well -
If you do think it's a good idea to have simple glazes - you had better
test your glazes before you use them on your ware. In the meantime it would
be a good idea to have a complex version - for when things go wrong.
It is quite a simple matter to substitute materials if you are using a
glaze calculator - and you have realistic analysis to work with.
I'll go a step further - If someone has a simple recipe they would like
complicated - I'll be happy to do the calculations if they will do the
testing and publish the results. It is not impossible to come out the other
side of an experiment like this and have a better glaze.
>----------------------------Original message----------------------------
>One more point on this - if you need (for instance) magnesium and whiting,
>why NOT use dolomite? Weighing out ingredients is tedious enough, why go
>for 6 if you can get it for 3? I am pursuing, in idle moments, a kind of
>holy grail of really simple and safe (but gorgeous, of course!) ^6 ox.
>glazes, with no more than 3 or 4 ingredients. I would love to get to the
>"pants pockets" measuring stage that mel talked about, but my gut feeling is
>that ^10 reduction pulls more out of the materials to make a simple glaze
>interesting at that temp. So far, my best ^6 ox. glazes usually have at
>least 6 and usually 8 or more materials in them. So - back to the question
>- if I can get two or three ingredients from one, of course I'll go for that
>one. Minor variations between batches have never been more than very minor
>in my experience - where I put it in the kiln usually has more effect.
>The only caveat, of course, is when there is a real sea-change in the
>quality of a material, like happened with colemanite.
Ron Roy
93 Pegasus Trail
Scarborough,Canada
M1G 3N8
Evenings, call 416 439 2621
Fax, 416 438 7849
Studio: 416-752-7862.
Email ronroy@astral.magic.ca
Home page http://digitalfire.com/education/people/ronroy.htm
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