Daraburn@AOL.COM on sun 6 feb 05
Had a customer order a black casserole and I don't normally do black but
agreed because I have used RR Black several yrs ago. Used the old RR Black and it
cracked and when fired it crawled badly. OK I wrote it off to maybe dust on
the bisque ware because it worked well before. Then I decided to mix a new
batch of Licorice using cobalt carb from a different supplier and got a deep
bluish black with some frost, but not the black I wanted. I am wondering if it
is the new cobalt carb: Does cobalt carb differ depending on the supplier?
Is some maybe not as "pure"? I have not had good luck with other oxides (Iron)
from this particular supplier so I am wondering. I have also noticed that
the raw color is different in their copper carb than that of another supplier.
Thanks,
Dawn in Tenn
John Anthony on mon 7 feb 05
Hi Dawn-
I have made many batches of Licorice (I have always been a fan of
Ron's black glazes - Old Black Magic is still my favorite on
porcelain). Licorice has always benn a black black for me- in direct
noon time summer sun you can see brown, and some flacks, but in any
normal light it's just black. I buy my iron and cobalt from Del Val
Pottery Supply in PA- 215 233 0655 is their number. Maybe they could
tell you the source of the chemicals and you could find a supplier
who could access the same stuff.
John A
http://www.redhillpottery.com
but not the black I wanted. I am wondering if it
> is the new cobalt carb: Does cobalt carb differ depending on the
supplier?
> Is some maybe not as "pure"? I have not had good luck with other
oxides (Iron)
> from this particular supplier so I am wondering. I have also
noticed that
> the raw color is different in their copper carb than that of another
supplier.
>
> Thanks,
> Dawn in Tenn
>
>
>
> Moderator of the list is Mel Jacobson who may be reached at melpots@p...
Kathi LeSueur on mon 7 feb 05
Daraburn@AOL.COM wrote:
>Had a customer order a black casserole and I don't normally do black but
>agreed because I have used RR Black several yrs ago. Used the old RR Black and it
>cracked and when fired it crawled badly..... I am wondering if it
>is the new cobalt carb: Does cobalt carb differ depending on the supplier?
>Is some maybe not as "pure"?.......
>
The problem may be with the cobalt, but the real problem is taking an
order for a glaze that you don't normally do. Taking orders for
different shaped or sized pots, assuming your skill level can handle it,
isn't a problem. But, it takes time to learn a glaze and all of its
problems. You can't just say well I used that glaze once or twice and it
worked so I can take this order. Glazing is complicated. Use glazes that
you know will work and avoid agreeing to do something you may or may not
be able to deliver on.
Kathi
John Hesselberth on tue 8 feb 05
Hi Dawn,
While no one can say for sure what caused your bluish black licorice,
the cobalt is certainly a possibility. It has been reported several
times here on Clayart that there is some poor quality cobalt being
offered for sale. Always buy your ingredients from a reputable supplier
who you trust--I do not recommend shopping on price for something as
important as this. In any case your cobalt carbonate should be a light,
bright lavender and a very fine powder--no graininess.
It also could be that you did not get the cobalt adequately dispersed.
I always screen at least twice through an 80 mesh screen. Three or 4
times if I have a difficult-to-disperse material like wollastonite.
Lastly, Kathy's comment is dead on. Taking orders for a glaze you don't
use regularly is high risk. There are just too many things that can
change with time.
Regards,
John
On Sunday, February 6, 2005, at 05:16 PM, Daraburn@AOL.COM wrote:
> Had a customer order a black casserole and I don't normally do black
> but
> agreed because I have used RR Black several yrs ago. Used the old RR
> Black and it
> cracked and when fired it crawled badly. OK I wrote it off to maybe
> dust on
> the bisque ware because it worked well before. Then I decided to mix
> a new
> batch of Licorice using cobalt carb from a different supplier and got
> a deep
> bluish black with some frost, but not the black I wanted. I am
> wondering if it
> is the new cobalt carb: Does cobalt carb differ depending on the
> supplier?
> Is some maybe not as "pure"? I have not had good luck with other
> oxides (Iron)
> from this particular supplier so I am wondering. I have also noticed
> that
> the raw color is different in their copper carb than that of another
> supplier.
>
> Thanks,
> Dawn in Tenn
>
> _______________________________________________________________________
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> Moderator of the list is Mel Jacobson who may be reached at
> melpots@pclink.com.
>
>
John Hesselberth
http://www.frogpondpottery.com
http://www.masteringglazes.com
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