ret on wed 9 apr 97
This mail from Monona came to me by mistake and was intended for the list.
Elke
I hope everyone reads what Karl Platt wrote in this post. The technical
concepts of equilibrium constants are something that I wish everyone
appreciated.
However, in the area of glaze leaching, these concepts are just that:
concepts. And predictions about shiny, buttery, matt, etc., are just that:
predictions. Glazes are such complex mixtures of chemicals in so many forms
and states that in the end, only testing will really tell you what is
happening. And then after we have enough hard data, we may be able to apply
the theories with better results.
Karl further wrote:
> I was thinking on the way over here today about the EPA Ba Drinking
> Water Standard -- it's 2 parts per million (PPM). This may be visualized
> as 2 grams in 1 million grams -- which is a metric ton. I'm stuck trying
> to think of a real-world example to demonstrate how REALLY small this
> is..... How about this:
> If you drank a 500 ml cup of this water every day you'd ingest 0.001
> grams of Ba. That is, you'd have to drink 1000 cups of water or 500
> litres (13 or so gallons) to ingest 1 gram of Ba from the liquid
> containing 2 ppm. <
This should sufficiently demonstrate how very little barium in the diet day
after day worries EPA enough to set the 2 ppm standard. ANd the 13 gallons
should also be considered in the light of the amount of liquid we consume
daily. My 1 gallon Brita gets filled every day for coffee, soup, etc. that I
consume. So if we are not talking about a single cup, but a set of cups,
pitchers, and bowls, the whole thing takes on quite another look.
> I also can't find any systematic studies on Ba leaching from glazes.
> Perhaps their absence reflects the exceedingly small (absent) nature of
> this "problem". If anyone else does discover any peer reviewed studies,
> pass them along here. I'm really burned out on reading all of this
> flakey anecdote that passes for authority. <
So say we all. THat's why many of us, like you, want the peer reviewed
studies and hard data to evaluate.
And what REALLY MAKES ME MAD is when people involved in the selling or
manufacturing of glazes or glaze chemicals can use the lack of data as a
reason to continue business as usual when THEY are the ones who should have
provided this data LONG ago. They make the profit. They and their trade
associations should have done the research already.
> This whole discussion about chemical durability raises questions in my
> mind about the merit of firing at cone 6. This seems to be an arbitrary
> standard in the potting world these days. I would suggest that if we
> were to move up to cone 8 a lot of these chemical durability issues go
> away by nature of the more "rigid" structures given by the lower alkali
> content of higher firing glazes. <
We don't know if this is true. Lets test this theory.
> This isn't to say that wholly satisfactory and durable glazes can't be
> made at cone 6. On the contrary, the tableware industry produced hotel
> china (bem resistente) with fritted lead glazes at cone 5 for decades *
> absolutely without incident*. <
Stuff and nonsense. Once again: we are not looking only for "incidents" of
acute poisoning. We are looking at leaching an amount of lead that will
add to the body burdens of users to their detriment. With this definition
firmly in mind, remember that the major Chinaware producers did not meet the
0.1 ppm California leaching standard (and which standard was also *proposed*
by FDA in 1989) until about 1992!!!
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/
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