[Clayart] Toxic Chems
lis.allison at primus.ca
Mon Aug 26 20:04:35 EDT 2019
Thank you, Robert. I had a vague idea it was as you say, but wasn't
sure. My physics and chemistry are from 50 years ago!
On 2019-08-26 5:27 p.m., Robert Harris wrote:
> 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
>> 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" *
>> * Don't call yourself a pilot until you have made*
>> * a night landing, in bad weather, on a WWll class
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