Charles G Hughes on mon 20 mar 00
------------------
I was recently presented with a bottle of silver carbonate...anyone know if =
it
has potential for use in a glaze?
I also have been gifted with lab grade Calcium Oxide. My understanding is =
that
it's mineral name would be Wollastonite and it is used similarly to Calcium
Carbonate but is perhaps 40=25 stronger. Can it be substituted for Calcium =
Carb at
a somewhat reduced percentage, or am I better off finding recipes that call =
for
it directly?
Thanks=21
Charles Hughes
http://www.thecreativeoasis.com
Tom Buck on tue 21 mar 00
If you do raku pots (or lowfire reduction) then silver carbonate is the
preferred (safe) compound to get "gold" from silver. Raku texts cite a
typical base glaze to which you add silver carbonate (and sometimes
bismuth subnitrate or similar bismuth compound). Do not overfire.
Use the lab-grade CaO (lime, caclium oxide) in place of whiting,
calcium cabronate, CaCO3. CaO mole weighs 56; CaCO3 mole weighs 100, so
adjust the weights as needed in the recipe. Wollastonite is Calcium
Silicate, CaSiO4.
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
Michael Banks on tue 21 mar 00
Charles,
Silver carbonate is useful for making lustres and is less corrosive than
silver nitrate.
Calcium oxide (quicklime or calcia) is a strongly basic (alkaline) oxide and
reacts with water releasing a lot of heat. As it is so caustic, it should
not be handled without hand and eye protection. Calcium oxide is not the
same as wollastonite (calcium silicate) and is probably too soluble and
caustic to use in glaze. Whiting (calcium carbonate) is de-carbonated above
825oC to calcium oxide anyway and should be concentrated enough to provide
any reasonable amount of lime to a glaze, as well as being a lot more
friendly to the user and insoluble too.
Michael Banks,
Nelson,
New Zealand
Charles G Hughes wrote:
----------------------------Original message----------------------------
I was recently presented with a bottle of silver carbonate...anyone know if
it
has potential for use in a glaze?
I also have been gifted with lab grade Calcium Oxide. My understanding is
that
it's mineral name would be Wollastonite and it is used similarly to Calcium
Carbonate but is perhaps 40% stronger. Can it be substituted for Calcium
Carb at
a somewhat reduced percentage, or am I better off finding recipes that call
for
it directly?
Thanks!
Kat Berger on tue 21 mar 00
Charles,
I have only used silver chloride, but this might be a place to start. I
mix silver chloride with an oil and bismuth subnitrate (James Chappell's
Clay and Glazes) for luster application. I would assume that any form
of silver is going to be a low-fire material burning out at 1200F or
somewhere in that range.
Remember that wollastonite is calcium and silica. Off hand, I believe
it's equal parts of each but don't quote me on that. They say that you
can substitute calcium and silica for wollastonite but I actually have
tried that and my glazes would come out slightly different. You know,
when the glaze just isn't working exactly the same. So, I assume that
in very touchy glazes it becomes difficult to substitute but in more
stable glazes you can.
Hope that helps
Kat in dreary Maryland
Ron Roy on mon 27 mar 00
I just worked this out - refer to my earlier post today about the ins
and outs of this process.
I have used real analysis for the materials I use. Wolastonite and
Whiting can vary from mine to mine - silica should vary little but it
will not hurt to check.
For every one part of Wolastonite my calculations say about 0.6
whiting and 0.4 silica. Part of the reason for this is the high LOI
of about 45% in whiting. You can also expect a little less melt
because the CaO and SiO2 in Wolastonite is already combined.
RR
>----------------------------Original message----------------------------
>
>Remember that wollastonite is calcium and silica. Off hand, I believe
>it's equal parts of each but don't quote me on that. They say that you
>can substitute calcium and silica for wollastonite but I actually have
>tried that and my glazes would come out slightly different. You know,
>when the glaze just isn't working exactly the same. So, I assume that
>in very touchy glazes it becomes difficult to substitute but in more
>stable glazes you can.
Ron Roy
93 Pegasus Trail,
Scarborough, Ontario
Canada. M1G 3N8
Tel: 416-439-2621
Fax: 416-438-7849
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