Veena Raghavan on wed 5 apr 00
There are quite a few recipes that call for magnesium carbonate. Is there
any substitute for this?
I would appreciate any advice from the glaze experts.
Thanks in advance.
Veena
Veena Raghavan
75124.2520@compuserve.com
Khaimraj Seepersad on thu 6 apr 00
Good Day to All ,
Veena ,
I use Magnesium Oxide when making Frits . I get
it from Ceramic Supply of New York And New
Jersey.
It is not fluffy or other and no carbonates to
decompose , not sure how it would behave in a
glaze .
There is also Talc , if you can factor the Silica and
other contaminants in .
A long shot Magnesium Zirconium Silicate .
AND Dolomite
But then again , are you asking to substitute for
Magnesium Carbonate with say Strontium Carbonate?
Khaimraj Seepersad
-----Original Message-----
From: Veena Raghavan <75124.2520@compuserve.com>
To: CLAYART@LSV.UKY.EDU
Date: 05 April 2000 13:07
Subject: substitute for magnesium carbonate
>----------------------------Original message----------------------------
>There are quite a few recipes that call for magnesium carbonate. Is there
>any substitute for this?
>I would appreciate any advice from the glaze experts.
>
>Thanks in advance.
>
>Veena
>Veena Raghavan
>75124.2520@compuserve.com
>
Craig Martell on thu 6 apr 00
Veena was wondering if:
>There are quite a few recipes that call for magnesium carbonate. Is there
>any substitute for this?
Hi:
I'm envisioning Ron Roy typing out the definitve answer to this query but
I'll post one anyway! :>)
Magnesium carb will contribute only Mg to a glaze after the carbonate is
liberated by heat. You can use Talc or dolomite in place of magnesium
carb. Talc contributes magnesia and silica to the glaze and dolomite
contributes magnesium and calcium so you have to use calculation to keep
the same molecular formula. If your glaze is devoid of calcia, you won't
be able to use dolomite. All glazes have some silica so talc is fine in
most cases. The short answer is that there are no raw materials that you
can substitute directly for magnesium carb. Well, none that I know of anyway.
regards, Craig Martell in Oregon
David Hendley on thu 6 apr 00
There are 2 good ways to substitute magnesium carbonate:
dolomite and talc.
Both are much, much cheaper.
The big hitch: dolomite adds calcium as well as
magnesium, and talc adds silica as well as magnesium.
So, to use talc you have to also decrease the silica, or
to use dolomite you have to decrease the whiting.
If your recipe does not use any whiting or silica that
you can reduce, then you can't make the substitution.
I make substitutions with glaze calculation, so I don't know
of a 'ratio' or formula for directly substituting, such as
'10 parts talc equals 3 parts magnesium carbonate
and 7 parts silica', but such a formula could probably be
worked out. Anyone?
--
David Hendley
Maydelle, Texas
hendley@tyler.net
http://www.farmpots.com/
----- Original Message -----
From: Veena Raghavan <75124.2520@compuserve.com>
To:
Sent: Wednesday, April 05, 2000 3:05 PM
Subject: substitute for magnesium carbonate
| ----------------------------Original message----------------------------
| There are quite a few recipes that call for magnesium carbonate. Is there
| any substitute for this?
| I would appreciate any advice from the glaze experts.
|
| Thanks in advance.
|
| Veena
| Veena Raghavan
| 75124.2520@compuserve.com
|
David Hewitt on fri 7 apr 00
MgO can be found in small amounts in many feldspars and ball clays and
in some frits. However the main alternatives to magnesium carbonate are
dolomite and talc. Dolomite also adds CaO and talc also adds silica. The
only regularly used material for just adding MgO is magnesium carbonate
( you can have magnesium sulphate). To use either or both dolomite or
talc, you would need to reformulate the recipe.
You don't say why you wish to make the change. What exactly is the
reason?
David
In message , Veena Raghavan <75124.2520@compuserve.com> writes
>----------------------------Original message----------------------------
>There are quite a few recipes that call for magnesium carbonate. Is there
>any substitute for this?
>I would appreciate any advice from the glaze experts.
>
>Thanks in advance.
>
>Veena
>Veena Raghavan
>75124.2520@compuserve.com
>
--
David Hewitt
David Hewitt Pottery ,
7 Fairfield Road, Caerleon, Newport,
South Wales, NP18 3DQ, UK. Tel:- +44 (0) 1633 420647
FAX:- +44 (0) 870 1617274
Web site http://www.dhpot.demon.co.uk
Smart on fri 7 apr 00
dear Veena Raghavan,
What is magnesium carbonate called for in your recipe? Is it used like main
recipe component (2,3 to 5 %) or just like minor component (0,1 to 0,5%..)?
Usually magnesium carbonate is used to floculate glazes slip at a rate of
0,1 to 0,2 %. Else in case of main component it's used to give magnesium
oxide to the glaze composition, but it gives bubbles if your glaze is a low
temperature glaze.
Answer me and perhaps I can help you.
I hope you understand my english, my french is better.
See my french ceramic site on : http://perso.wanadoo.fr/smart2000/
It's only written in french, but there are pictures...
Cordialement,
Smart
----- Original Message -----
From: Veena Raghavan <75124.2520@compuserve.com>
To:
Sent: Wednesday, April 05, 2000 10:05 PM
Subject: substitute for magnesium carbonate
> ----------------------------Original message----------------------------
> There are quite a few recipes that call for magnesium carbonate. Is there
> any substitute for this?
> I would appreciate any advice from the glaze experts.
>
> Thanks in advance.
>
> Veena
> Veena Raghavan
> 75124.2520@compuserve.com
June Perry on fri 7 apr 00
Veena:
To add to Craig's list, there's also mangnesium oxide, but you might have to
check around to find it. It would probably be easier to just reformulate the
glaze for talc or dolomite if the glaze has calcium, as stated so well by
Craig. :-)
Warmest regards,
June
Tom Buck on sun 9 apr 00
Original question: what will replace magnesium carbonate (MgCO3). And
David Henley asked for equalivalent values for Talc and Dolomite as
substitutes.
To do the subs, one does it on a molar basis, namely,
1 mole MgCO3 sypplies 1 mole MgO in the fired glaze.
So, 1 mole of Dolomite (MgCO3.CaCO3) supplies 1 mole MgO and 1 mole CaO.
Plus a bit of "bound water", 1.5% often.
And 1 mole Talc (MgO.SiO2) supplies 1 mole MgO and 1 mole SiO2.
Talc, however, usually has some "bound water" with the MgSiO3 (often 5.5%)
As result the weight equivalences are:
Dolomite has a mole weight 184.4, add water = 187.2
Talc has a mole weight of 100.4, add water = 102.6
MgCO3 has a mole weight of 84.3. And it usually is of high purity with no
water.
So to sub for MgCO3 in a recipe: Divide the weight by 84.3 and if
you use Talc multiply the answer (= to No. of moles) by 102.6. This gives
the amount of Talc needed in the recipe. Then if you divide the amount of
Silica (Flint) by 60 you find the No. of moles of it, and you subtract
this amount by the number of moles Talc, and then using this new number of
Silica/Flint moles, remulitply by 60 to find the NEW weight value for
Silica/Flint.
The same applies to Dolomite only this time you adjust the amount
of Whiting (or Wollastonite) in the same way.
The maths are not hard, just the problem of keeping track of the
steps to make sure it gives the proper results.
Good pots. BFN. 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
Ron Roy on sun 9 apr 00
Hi Veena,
As others have stated - the usual way to do this is to use either Talc or
Dolomite depending on the other oxides needed in the glaze.
It works the other way as well - if you wanted crawling and you had enough
MgO in the glaze from either Talc or Dolomite you could take them out and
sub in Magnesium Carb.
To get the same glaze use calculation software (or do it with a calculator)
by matching up the oxides in the molecular formula.
I often do this for potters who are having crawling problems with glazes
due to the presence of MgCO3 - not a difficult job if the analysis of
Dolomite and Talc are reasonably accurate.
RR
>----------------------------Original message----------------------------
>There are quite a few recipes that call for magnesium carbonate. Is there
>any substitute for this?
>I would appreciate any advice from the glaze experts.
>
>Thanks in advance.
>
>Veena
>Veena Raghavan
>75124.2520@compuserve.com
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Dannon Rhudy on mon 10 apr 00
At 08:53 PM 4/9/00 EDT, you wrote:
>----------------------------Original message----------------------------
>Original question: what will replace magnesium carbonate
>..... To do the subs, one does it on a molar basis, namely,
> 1 mole MgCO3 sypplies 1 mole MgO in the fired glaze.
>So, 1 mole of Dolomite (MgCO3.CaCO3) supplies 1 mole MgO and 1 mole CaO.
>Plus a bit of "bound water", 1.5% often.
>And 1 mole Talc (MgO.SiO2) supplies 1 mole MgO and 1 mole SiO2.
>Talc, however, usually has some "bound water" with the MgSiO3 (often 5.5%)
> .> .............
------------------------------------------------
Tom Buck, you cannot know what a treasure you are, how
clear your explanations, how interesting your information,
how generous you are with your time. A public thank you
is in order - here's mine.
best regards,
Dannon Rhudy
potter@koyote.com
Veena Raghavan on tue 11 apr 00
David,
You must think me awfully rude if you did not get the message
below. I am resending it just in case:
Message text written by David Hewitt
>MgO can be found in small amounts in many feldspars and ball clays and
in some frits. However the main alternatives to magnesium carbonate are
dolomite and talc. Dolomite also adds CaO and talc also adds silica. The
only regularly used material for just adding MgO is magnesium carbonate
( you can have magnesium sulphate). To use either or both dolomite or
talc, you would need to reformulate the recipe.
You don't say why you wish to make the change. What exactly is the
reason?
David<
------
Hi David,
Thank you for your response. The reason I was trying to substitute
is that I do not have any magnesium carbonate, am not ordering any
chemicals at present, one reason being that I might be moving from New York
to Virginia in the next few months, and I am trying to keep things down. I
do not have scales at home and am leaving the studio where I weight out my
materials in the next couple of months with no other studio lined up. In
other words, I am in a state of suspension at present, but still want to
keep testing glazes, making pottery, and keep my sanity.
I do not have a glaze calculation program and have next to no
knowledge in this area. I am hoping to get to a good glaze making workshop
in the near future (Ron Roy or Ian Curry would be great), but at present I
am just testing glazes generously shared on Clayart or from books, and when
they don't work, I just have to move on.
One of the glazes I wanted to try was:
Klinesville Gold ^6 ox
magnesium carb. 359.2
whiting 1618.4
wollastonite 449.6
neph sy 4494.4
cedar hts. red art 1078.4
red iron ox 539.2
zircopax 988.8
Tom Buck very kindly put this through his glaze calculation program and
sent me the following:
You seek a "gold" at C6...well this is not a balanced glaze and it
will likely craze on most bodies....If however you want an outside mix for
a vase etc, then ok. But it won't be food-durable (not likely poisonous
though exzcept for women who shouldn't be taking too much iron).
Here is a recipe using talc:
C6 Ox K Gold
86 Talc
188 Whiting
52 Wollastonite
521 Neph Sy
155 REDART
64 Iron Oxide red
120 Zircopax
Ratio is 6 (matt) and Expansion is 8.4 too high for most bodies.
But it may be what you want.
-----------------------------------------
Actually, the glaze, which was on Clayart, is described as wonderful light
brown, almost looks like a high fire rutile glaze with blue and purple in
it.
It sounded interesting and I wanted to try it for my non-functional ware.
Thank you again for responding.
If you would be interested in the results I get from this reformulated
glaze, do let me know.
All the best.
Veena
Veena Raghavan
75124.2520@compuserve.com
Ron Roy on tue 11 apr 00
Yes - Craig is right - I can't just go by this kind of thing. Here is a
sample of what this is all about. I inveted a glaze - probably cone 10 -
real stiff glaze but good for what I want to show.
G200 - 50.0
Mag Carb - 5.0
Whiting - 10.0
EPK - 10.0
Silica - 25.0
Total - 100.0
Ratio - 8.25
Expansion - 472.03
Took out the MgCO3 and replaced the MgO with Talc. Big surprise - had to
lowe the CaO because the analysis for the talc I use has a significant
abmout of CaO.
This is pretty much the same glaze but with a little better melt because
the MgO and Silica in the Talc are already combined.
G200 - 50.0
Talc - 8.0
Whiting - 9.0
EPK - 10.0
Silica - 21.0
Total - 98.0 < blame the loss on the LOI of Mag Carb at 52.38
Ratio - 8.29
Expansion - 472.72
The dolomite version is a surprise too - had to take out some clay because
the dolomite I use has some alumina.
G200 - 50.0
Dolomite - 11.5
Whiting - 3.5
EPK - 9.5
Silica - 25.5
Total - 100.0 < bact to 100 because the loss on my dolomite is 45.53
Ratio - 8.38
Expansion - 472.04
So this is fairly difficult to just eyeball - calculation is the right way
to go if you want to get there fast. Gives you the added advantage of
monitoring the expansion and ratio as well.
Take a look at the calculated expansions for the three glazes - gives some
idea of just how accurate calculation can be. If anyone would like to
actually fire these up at cone 10 - put em in the hot part of your kiln -
with a cone beside them - maybe add 2% iron to see if what we have is a
celadon. Let us know if these are really the same glaze.
RR
>----------------------------Original message----------------------------
>Veena was wondering if:
>>There are quite a few recipes that call for magnesium carbonate. Is there
>>any substitute for this?
>
>Hi:
>
>I'm envisioning Ron Roy typing out the definitve answer to this query but
>I'll post one anyway! :>)
>
>Magnesium carb will contribute only Mg to a glaze after the carbonate is
>liberated by heat. You can use Talc or dolomite in place of magnesium
>carb. Talc contributes magnesia and silica to the glaze and dolomite
>contributes magnesium and calcium so you have to use calculation to keep
>the same molecular formula. If your glaze is devoid of calcia, you won't
>be able to use dolomite. All glazes have some silica so talc is fine in
>most cases. The short answer is that there are no raw materials that you
>can substitute directly for magnesium carb. Well, none that I know of anyway.
>
>regards, Craig Martell in Oregon
Ron Roy
93 Pegasus Trail
Scarborough
Ontario, Canada
M1G 3N8
Evenings 416-439-2621
Fax 416-438-7849
Charles G Hughes on wed 12 apr 00
Ok here is a question for you along the same lines. I have a lot of
Magnesium Oxide. Can I use this in a glaze, or is it somehow soluble and
dangerous the way Calcium Oxide is?
-Charles
----- Original Message -----
From: Ron Roy
To:
Sent: Tuesday, April 11, 2000 3:15 PM
Subject: Re: substitute for magnesium carbonate
> ----------------------------Original message----------------------------
> Yes - Craig is right - I can't just go by this kind of thing. Here is a
> sample of what this is all about. I inveted a glaze - probably cone 10 -
> real stiff glaze but good for what I want to show.
>
> G200 - 50.0
> Mag Carb - 5.0
> Whiting - 10.0
> EPK - 10.0
> Silica - 25.0
> Total - 100.0
> Ratio - 8.25
> Expansion - 472.03
>
> Took out the MgCO3 and replaced the MgO with Talc. Big surprise - had to
> lowe the CaO because the analysis for the talc I use has a significant
> abmout of CaO.
> This is pretty much the same glaze but with a little better melt because
> the MgO and Silica in the Talc are already combined.
>
> G200 - 50.0
> Talc - 8.0
> Whiting - 9.0
> EPK - 10.0
> Silica - 21.0
> Total - 98.0 < blame the loss on the LOI of Mag Carb at 52.38
> Ratio - 8.29
> Expansion - 472.72
>
> The dolomite version is a surprise too - had to take out some clay because
> the dolomite I use has some alumina.
>
> G200 - 50.0
> Dolomite - 11.5
> Whiting - 3.5
> EPK - 9.5
> Silica - 25.5
> Total - 100.0 < bact to 100 because the loss on my dolomite is 45.53
> Ratio - 8.38
> Expansion - 472.04
>
> So this is fairly difficult to just eyeball - calculation is the right
way
> to go if you want to get there fast. Gives you the added advantage of
> monitoring the expansion and ratio as well.
>
> Take a look at the calculated expansions for the three glazes - gives some
> idea of just how accurate calculation can be. If anyone would like to
> actually fire these up at cone 10 - put em in the hot part of your kiln -
> with a cone beside them - maybe add 2% iron to see if what we have is a
> celadon. Let us know if these are really the same glaze.
>
> RR
>
> >----------------------------Original message----------------------------
> >Veena was wondering if:
> >>There are quite a few recipes that call for magnesium carbonate. Is
there
> >>any substitute for this?
> >
> >Hi:
> >
> >I'm envisioning Ron Roy typing out the definitve answer to this query but
> >I'll post one anyway! :>)
> >
> >Magnesium carb will contribute only Mg to a glaze after the carbonate is
> >liberated by heat. You can use Talc or dolomite in place of magnesium
> >carb. Talc contributes magnesia and silica to the glaze and dolomite
> >contributes magnesium and calcium so you have to use calculation to keep
> >the same molecular formula. If your glaze is devoid of calcia, you won't
> >be able to use dolomite. All glazes have some silica so talc is fine in
> >most cases. The short answer is that there are no raw materials that you
> >can substitute directly for magnesium carb. Well, none that I know of
anyway.
> >
> >regards, Craig Martell in Oregon
>
> Ron Roy
> 93 Pegasus Trail
> Scarborough
> Ontario, Canada
> M1G 3N8
> Evenings 416-439-2621
> Fax 416-438-7849
Evan Dresel on wed 12 apr 00
I do wonder how anyone comes up with a glaze that contains magnesium
carbonate and whiting. A theoretical substitution is:
For each 1 g of magnesium carbonate to be removed, remove 1.096 g of
whiting and add 2.019 g of dolomite. Personally I'd try rounding the
numbers to 1.1 g whiting and 2.1 g dolomite then adjust from there.
This doesn't account for minor impurities.
-- Evan in W. Richland WA who thinks dolomite is a way cool mineral.
Still a lot of questions about how it forms, and the ordered crystal
structure with layers of calcium alternating with layers of magnesium is
fairly unique among carbonates.
Veena Raghavan wrote:
>
> ----------------------------Original message----------------------------
snip...
>
> One of the glazes I wanted to try was:
>
> Klinesville Gold ^6 ox
>
> magnesium carb. 359.2
> whiting 1618.4
> wollastonite 449.6
> neph sy 4494.4
> cedar hts. red art 1078.4
> red iron ox 539.2
> zircopax 988.8
>
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