[Clayart] Toxic Chems

Robert Harris robertgharris at gmail.com
Mon Aug 26 17:27:01 EDT 2019

OK as a scientist who sat through more OSHA and lab safety talks than I
care to remember I have a few comments.

1.  The plural of anecdote is not data. Just because you didn't seem to
suffer doesn't mean it's a problem. Statistics .... statistics ...
statistics. That is the only way we can determine how widespread a problem
this is.

2. Almost all "toxic" chemicals are only toxic to us, when they become
water (or fat) soluble.

Barium is still sometimes used as a contrast agent in radiology for gut
health (so called Barium meal). This is Barium sulfate which is extremely
insoluble. Barium Carbonate is pretty insoluble although it can get
attacked by acids and form something more soluble (eg Barium Chloride from
attack by Hydrochloric acid). Since you have lots of Hydrochloric acid in
your stomach this can be an issue if you suck your fingers a lot. At this
point it becomes much more dangerous to potters. Likewise the lead everyone
used in the 40s was a fritted Lead silicate if some sort. This is very
insoluble and resistant to acids and isn't much of a problem for pottery
workers. Where there is an issue (and of course the whole focus of Ron Roy
and John Hesselberth's research - for materials other than lead), is when a
poorly designed glaze allows the lead to be leached out (in a soluble
form!) by acids. Lead exposure in potteries WAS a real problem in the late
18th century, when they were still using Litharge, Red lead, and Galena all
of which can dissolve when ingested. Lifespan of inudstrial potters in the
late 18th century was so low that there were strikes (in England) over the
use of lead - it was significant enough they didn't need statistics to
figure out there was a problem. This led to Zinc based "Bristol" glazes. as
well as invention of safer, fritted forms of lead.
Chromium and Cobalt are also toxic, but the forms we use are insoluble
(some people use Cobalt Sulphate which is soluble, but as long as you don't
suck your brush it's not too much of a problem). Manganese is also toxic as
we all know, but it is likely that the biggest problem for potters is not
skin exposure, but rather the fact that it volatilizes in the firing and if
your kiln is nearby what you breathe in is highly toxic and easily
absorbed. (Same problem as lead in gasoline - very easily absorbed once

The mistake far too many people make is seeing these elements as all being
the same thing, in terms of toxicity. We never actiually see them in
elemental form (I'll ignore everyone that has lots of chrome on their car!)
While it is true that it is the elements that make them toxic, we only need
to be concerned at specific compounds of the element. When looking at our
glaze materials the real issue is that word that multi-vitamin companies
love ... bio-availability.

So please don't dismiss the toxicity of various metals but instead consider
the form they are in, in your workshop, and educate yourself on when they
can become dangerously bioavailable. (Zinc fuming is another example).


On Sat, 24 Aug 2019 at 16:12, Jim Brown <jbrown1000 at gmail.com> wrote:

>  Toxic this? Toxic that! " - David
> I have never understood the, many times, hysteria about pottery and toxic
> chemicals.  If even a small part of what has been said by many were true I,
> and many, many others would have been dead in our early 30's or so.
> Grandpa used lead based cone 04 glazes for years on part of the products he
> made and cone 6 - mostly Albany Slip - on the "older" type wares.  The lead
> based glazes were mixed in large - I believe #2 - tubs and many times this
> was stirred using our hands with the glaze going up past our elbows.  The
> glazed pieces were finished - mostly the bottoms given a quick wipe to take
> off what little glaze was on the waxed areas - and over the years the whole
> area where this was done was covered in red brown glaze dust.
> The back of the shop was where the native clay was crushed into a fine
> powder then pugged and dust from that was everywhere - never heard of a
> respirator.
> If I suffered any brain problems from the lead or other chems, I must have
> been the smartest person ever to have lived before the damage because I
> went on to become a Naval Officer and Pilot and for the first 75 years of
> my life had virtually no medical problems and the ones I have had since
> have nothing to do with either toxic chemicals or dust.
> By the way, when the "big lead scare" came about and the government came
> around and tested all of Grandpa's glazes, they all passed without a
> problem so if formulated properly and burned properly lead glazes can be
> safe.  But Grandpa, like virtually everyone else due to the publicity,
> stopped using lead based glazes.
> Just sayin'.
> *                                    JIM BROWN*
> *                             BROWN POTTERS*
> *                  "Making handmade pottery . . . *
> *                                                                  . . .
> since the 1700's" *
>                           *www.brownpotters.com
> <http://www.brownpotters.com>*
> *                        Don't call yourself a pilot until you have made*
> *                  a night landing, in bad weather, on a WWll class
> carrier*
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