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copper carbonate (now material quality)

updated fri 18 oct 02


John Hesselberth on thu 17 oct 02

Hi Dan,

You could try hand grinding it with a mortar and pestle (dust mask
firmly in place), but frankly I'd look for a different supplier. Try
Del Val on the north side of Philly. They are not too far from you and
carry high quality materials.

That brings me to a related point I have been wanting to make for some
time. We potters are generally not wealthy people and we know how to
squeeze a nickel pretty well. Sometimes that pays and sometimes it
doesn't. Glaze materials is one area where you have to be really
careful. There are some really low grade materials being sold out there
for seemingly bargain prices. I am not condemning all low priced
materials. Undoubtedly some suppliers have lower costs or are willing to
work at lower margins than others. But OUR continual price shopping
also causes some people to buy and resell lower quality materials in
order to be price competitive and still make a profit.

In particular, be careful to ask for analysis sheets and quiz your
supplier on the quality of things like cobalt carbonate/oxide, copper
carbonate/oxide and other of the more expensive materials. You probably
don't have to worry much about things like feldspars or clays or even

We have had relatively few people have trouble reproducing (or nearly
so) the glazes in our book, but of those who have had trouble we have
traced nearly all to either firing conditions (primarily cooling rate,
but sometimes over/underfiring) or materials quality. The materials
causing the most problems have been cobalt carbonate, copper carbonate
and rutile.

I am interested in collecting information on supply source vs. your
results--I am interested not so much in who you bought it from but who
the original supplier was--grade and lot number--to see if I can figure
out which materials are giving the best results.

As an example, my supplier is Judy Wilson who owns Del Val. She buys
most of her chemicals from Standard Ceramic. Judy currently sells
cobalt carbonate for $24-25/lb--at least that is the price in her last
catalog. I can find ads for that material at $18-20/lb. Would I buy
from them? Not on your life. I know Judy has quality materials and it
is just not worth taking the chance. I am sure there are other quality
suppliers out there who will not compromise quality for price and maybe
even the $18-20 cobalt is just fine. But I also know there is some
garbage floating around out there that is loaded with impurities. My
real point is: get to know your supplier to the point where you can
trust that he/she is buying and selling quality materials. Ask her for
analysis sheets. Ask if they have changed suppliers since you last
bought that material. The vast majority of these folks are people who
care and will answer the above questions forthrightly. If they don't,
well, it might be time to look for a different supplier. And please,
don't just buy something as expensive as, say, cobalt carbonate and
assume it is all the same stuff. It just isn't.

I would love to hear from the suppliers who monitor the list regarding
this issue. I know you are under difficult competitive pressure, but
let us know your perspective.



On Thursday, October 17, 2002, at 09:19 AM, Dan Bowen wrote:

> I do not have a ball mill. How do keep it in
> suspention or do I need to find a suplier with the lighter green color.