Monona Rossol on sat 10 jan 98
---------- Forwarded message ----------
Date: Thu, 8 Jan 1998 11:07:37 EST
From: Ron Roy
Subject: Re: vanadium encapsulation.
>----------------------------Original message----------------------------
>>Ron: The stain manufacturers all say that Vanadium containing stains
>>should not be fired over 1250 degrees Celsius, so I'd conclude that this
>>is the temperature at which the encapsulation breaks down for stains with
>>Vanadium in them. There are other warnings in the "small print" that
>>usually accompanies stain literature. Til later.Peace. Tom Buck
> Thanks Tom - I think they must also say no abrasion as well. I am wondering
> - in a soft glaze will stirring wreck the encapsulation - wish I kew more
> about this. < Ron Roy
The data that I've seen was on silica encapsulated cadmium pigments. The
animal tests showed a slowed in uptake in the gut but they sure weren't
non-toxic. This means that stomach acid and other mechanisms break down the
"encapsulation." By inhalation--no difference to speak of. The pigment
industry tried to get OSHA to remove the encapsulated cadmium pigments and
other cadmium pigments from regulation under the Cadmium Standard. OSHA
looked at the data and didn't buy it even a little bit.
And when the "encapsulation" is silica, my assumption is that it will
be chewed up just like any other source of silica in glazes. If this is
the case, the fluxes in each glaze will attack the colorants differently.
If I was under oath and had to give an opinion about what I thought an
"encapsulated" pigment was, I'd have to say, "a frit with a press agent."
I'll bet a cookie that vanadium, cadmium, and other colorants aren't
"encapsulated" with with a neat little layer of silica around them. I'll be
they are just mixed with stuff, melted and reground. Makes them cheaper
than the raw pigments, too.
Monona Rossol, industrial hygienist
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York, NY 10012-2586 212/777-0062
http://www.caseweb.com/acts/
Karl P. Platt on mon 12 jan 98
> If I was under oath and had to give an opinion about what I thought an
> "encapsulated" pigment was, I'd have to say, "a frit with a press agent."
> I'll bet a cookie that vanadium, cadmium, and other colorants aren't
> "encapsulated" with with a neat little layer of silica around them. I'll be
> they are just mixed with stuff, melted and reground. Makes them cheaper
> than the raw pigments, too.
Actually, you would be correct in the assumption that the pigments aren't
encapsulated in silica. They are encapsulated in Zirconia. They are also
genuinely encapsulated and they are not cheap.
The patent literature can be consulted for details as to how these
pigments are produced and used. I don't have the address here, but IBM
maintains a site replete with all patenta issued since 1975 or so.
ALternatively, it would be well to consult Cerdec, Inc which produces this
class of pigments and has extensively tested their behaviors in all
respects.
KPP
Monona Rossol on thu 15 jan 98
---------- Forwarded message ----------
Date: Mon, 12 Jan 1998 13:54:24 EST
From: "Karl P. Platt"
To: Multiple recipients of list CLAYART
Subject: Re: vanadium encapsulati
---------------------------Original message----------------------------
>> If I was under oath and had to give an opinion about what I thought an
>> "encapsulated" pigment was, I'd have to say, "a frit with a press agent."
>> I'll bet a cookie that vanadium, cadmium, and other colorants aren't
>> "encapsulated" with with a neat little layer of silica around them. I'll
>> be they are just mixed with stuff, melted and reground. Makes them
>> cheaper than the raw pigments, too.
> Actually, you would be correct in the assumption that the pigments aren't
> encapsulated in silica. They are encapsulated in Zirconia. They are also
> genuinely encapsulated and they are not cheap. <
The pigments that were being discussed at the time the OSHA Cadmium Standard
was in comment period were "silica encapsulated cadmium pigments." They were
tested by ingestion in dogs and the test results were not impressive at all.
And in fact, this was about all the data on them that existed. Very poor
information, to say the least, for a product that was being used in a number
of industries. The same lack of data also was true for un-encapsulated
cadmium pigments! It was also depressing that the few studies that did exist
were "industry studies" done under less than strict protocol and
unpublished.
This is not just my opinion. In the preface to the OSHA Lead Standard, OSHA
referred to the cadmium pigment studies and explained the problems with them
in detail. As a result, OSHA rejected the premise that any of the cadmium
pigments were any safer than other cadmium sources. The pigments are fully
included in the OSHA cadmium regulations.
On the zirconia encapsulated pigments: I have not seen any data. But the
data isn't published in major peer-reviewed journals and lying around for
people to consult, that much I am pretty sure of.
...it would be well to consult Cerdec, Inc which produces this
> class of pigments and has extensively tested their behaviors in all
> respects. <
I've taken a look at Cerdec in Washington, PA, and so far it appears that the
primarily the distributor for Cerdec *France* where many of the "stains,
glaze frits, colors, precious metal preparations, heavy metal-free products
and glass enamels" are made (quote from the Ceramic Industry's Buyer's
Guide). They distribute Drakenfield Products--for those who know about this
line.
Usually it is difficult to get good information from companies who distribute
for a foreign Co. (as I have found in trying to get data from Sennelier,
Rembrandt, Kremer, etc., etc.), but I am trying. Today, so far, no one is
available to answer my questions, but I called at a bad time and have been
given the extension No.s of two people there who are supposed to know. I
will call back and report to Clayart when I know more.
Monona
Arts, Crafts and Theater Safety
181 Thompson St., # 23
New York NY 10012-2586 212/777-0062
http://www.caseweb.com/acts/
| |
|
