David Hendley on tue 8 may 01
Dear Hudson (ha)
Here are some of my responses to past questions about
cadmium inclusion stains.
I also use these stains as an overglaze pigment by adding
20% stain to stiff glaze base.
| ----------------------------Original message----------------------------
| Anyone know how these encapsulated cadmium stains stand up in ^8 and up
| glazes? Are they foodsafe in all circumstances?
|
They seem to stand up to anything.
I regularly fire them to cone 10 - 11 in my wood-fired
kiln - red and yellow.
The manufacturer claims that they are foodsafe in all
circumstances; the cadmium is 'bound' by zirconium and
silica, so it cannot leach even in a defective glaze.
I wouldn't bet my (or my customer's) life on it.
The only responsible thing to do is either:
----use the stains only on non-contact, non-leachable
surfaces, or,
----have your glaze tested for cadmium release, if you
use the stains in a food-contact glaze.
I have been using the Cerdec encapsulated cadmium stains for years.
There are 4 colors: intensive red, Bordeaux red, orange, and yellow.
I use them at cone 10+ in a wood-fired kiln, and the color still holds
up. This is pretty remarkable; the only tougher test I can think of
would be to try them at cone 10 in a wood-fired salt or soda kiln.
Generally speaking, the colors stay bright primary colors in a
low-fire oxidation situation. Higher temperatures and reduction,
as you would expect, mute the bright colors to more earthy tones,
but they are still, without a doubt, red, orange, and yellow that
are unattainable via any other route at cone 10 reduction.
In this atmosphere, it takes quite a bit of stain for good saturated
color, about 8 - 10% in a glaze, and 12 -15% in a slip.
This gets expensive in a hurry, with the stains selling for about
$40 a pound. I don't know, but I think you would be able to
get by with less as you fire in oxidation at lower temperatures.
The manufacturer claims that these stains are food-safe, but I
treat them as the dangerous cadmium that they are. That means being
extra careful with the raw stains, and using them only on non-food-
bearing pottery surfaces.
In fact, except for some tests, I only use the stains in slip-glazes
that I brush on the exterior of pots. This serves the dual purpose
keeping them away from food contact points, and making a little
stain go a long way. One pound of stain will glaze or decorate
hundreds of pots used this way.
I've also found it unnecessary to keep the orange stain on hand; if
I want orange, I can just mix red and yellow. The two reds are
a little different and I would suggest you try both, to see which you
prefer, and then buy only that one.
----- Original Message -----
From: Hudson Mackenzie
To:
Sent: Tuesday, May 08, 2001 1:35 PM
Subject: Encapsulated stains
| from Mark Harari (SirClayfoot@aol.com) via hudson@potters.org
|
| Hi everyone,I've just recieved a shipment of encapsulated red mason
stain. This stuff is made of cadmium but is supposed to be food safe. Im
doing some testing right now trying to determine what percentages to add to
my clear to get a strong red. Also, has anyone out there used this as an
overglaze pigment? If so what are you using to flux it? Im firing to cone
6-7 in oxidation. Any info that anyone can furnish would be most
appreciated. Thanks Mark
|
Tom Buck on tue 8 may 01
Mark:
The zircon encapsulated stains containing cadmium (or lead), while
safe for a potter to handle (excluding inhaling the stuff), cannot be
judged safe after firing. Here is what my supplier says:
"Cadmium and lead bearing stains: Not recommended for use on food
surfaces unless testing establishes that the glazed product meets
standards set by hazardous products (glazed ceramics) regulations."
This topic has been discussed many times in recent years, and
there is some evidence that the encapsulation may become defective when in
contact with some molten glazes.
So, exercise due caution, please.
bye. 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
Hudson Mackenzie on tue 8 may 01
from Mark Harari (SirClayfoot@aol.com) via hudson@potters.org
Hi everyone,I've just recieved a shipment of encapsulated red mason stai=
n. This stuff is made of cadmium but is supposed to be food safe. Im do=
ing some testing right now trying to determine what percentages to add to=
my clear to get a strong red. Also, has anyone out there used this as a=
n overglaze pigment? If so what are you using to flux it? Im firing to =
cone 6-7 in oxidation. Any info that anyone can furnish would be most app=
reciated. Thanks Mark
mel jacobson on thu 13 sep 01
i see in a full page ad in the new `ceramic bulletin` that
mason is making a high temp stain in bright reds and orange.
www.ceramics.com/mason
mel
From:
Minnetonka, Minnesota, U.S.A.
web site: http://www.pclink.com/melpots
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