Frank M. Gaydos on fri 12 nov 99
Any opinions on the reliability of the home test kits for lead,(heavy
metals).
I have an old Fran/Don lead release test kit in the studio and the basic
principal seems to work like this;
Like most of the advice on this list for testing glaze reliability, you
glaze a small bowl form with the glaze to be tested. Then add white vinegar
to the container and let sit covered for 24 hours. Dump the contents and
examine the glaze in the form.
Normally you would just look at the glaze for visible signs of leaching like
pitting or loss of color.
The test kits go a step further by adding a few drops of Sodium Sulfide or
Potassium Sulfide to the vinegar.
I believe the Sulfides make visible any heavy metals in the vinegar which
will look like yellow or brown or black clouds. On the Fran/Don container,
they state if the color is black then that is lead that has been released.
Also, on the Fran/Don label they claim a patent. Since this testing
procedure is a standard in the chemistry labs, I believe the patent is for
the advice that they give, suggesting you pour the vinegar into a small
white plastic container to achieve better contrast when the Sulfides are
added.(Not really sure about that)
This test procedure will give a general result only. That is, that yes,
something is leaching or no, the glaze is stable. It also will not tell you
what exactly is leaching unless you use deductive reasoning. (Sometimes)
I'm curious how accurate this test is.
Well, that's the pitch, anyone want to take a swing at it?
PS The test kits are very expensive for what they offer. I'm sure the
Sulfides can be purchased for a few dollars, not the tens of dollars some of
the kits charge.
Frank Gaydos
510 Gerritt St.
Philadelphia, Pa.
19147-5821
HTTP://home.earthlink.net/~fgaydos/
Paul Lewing on sat 13 nov 99
I can't comment on the reliability of home tests for lead leaching, but
I do know that you don't have to purchase a kit. In my old copy of
Harry Fraser's "Glazes for the Craft Potter" there is a description of
the test and the chemicals you need, all of which you can get at the
drugstore. I haven't seen the recently reissued version of this book,
but I'd bet it's still in there. Great book, by the way.
Paul Lewing, Seattle, where the rains have begun in earnest. Oh, well,
can't complain. Summer was a real dissapointment this year, but we've
had one of the most beautiful falls I've ever seen here.
Martin Howard on tue 16 nov 99
Paul Lewing says:-
In my old copy of
Harry Fraser's "Glazes for the Craft Potter" there is a description of
the test and the chemicals you need, all of which you can get at the
drugstore. I haven't seen the recently reissued version of this book,
but I'd bet it's still in there. Great book, by the way.
Yes, Paul and all. It is still there. Still a great book. Has anyone on list
actually followed it through and did they find any problems.
Incidentally, Harry is joining the list. Give him a good welcome. I have
found him very helpful for answering all sorts of problems.
Martin Howard
Webbs Cottage Pottery
Woolpits Road
Great Saling
BRAINTREE
Essex CM7 5DZ
martin@webbscottage.co.uk
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