Gavin Stairs on fri 6 mar 98
Hi All,
As this thread has come up again, I thought I'd pass on the following: I
found the official references for this test on-line. These tests are
specific for Cadmium and Lead only. I have not found any other metals
referred to in the FDA CPG (see below). C 738 specifies a complete
procedure requiring 6 pots, leaching for 24 hours in the dark at room
temperature, and concentration determination by atomic absorption
spectroscopy (AAS).
The reference document at FDA is available free on the web at
It is called "COMPLIANCE POLICY GUIDES, (August 1996 edition), Updated
Through October 31, 1996." Look in: CHAPTER 5 - FOODS; SUB CHAPTER 545 -
FOOD RELATED; 545.400 Pottery (Ceramics) - Cadmium Contamination CPG
7117.06 Page 241 and
545.450 Pottery (Ceramics) - Lead Contamination CPG 7117.07 Page 234.
The test should be referred to as ASTM C 738. Available for US$17.00 by
download from the ASTM web site. Go to the on-line
store and search for C738. The current document is C 738 - 94.
For potters who wish to comply (it's the law in the US at least), they will
have to test any ware that is suspect by the specific test for the metal,
either Cadmium or Lead. I can't imaging this costing less than US$100 per
test in the US, but maybe someone has a better source.
There is need for an indicative test: one that will show whether a glaze is
suspect or not, and which can be done for much less than the precise,
elemental assay. I suspect that a residue test can be devised which would
do this. By this I mean to leach per C738, but to evaporate to residue
under vacuum (to preserve volatile lead in particular), and then weigh the
residue as acetate. This has many defects as an assay, but it has the
great benefit of being cheap and requiring relatively cheap apparatus. The
test would show all leach products, including relatively benign ones like
Si and Al. Essentially, the good result in a test like this is a null
result.
If the pot fails this test, and your glaze contains either Cd or Pb, you
need to do the ASTM C 738 to see how much Cd or Pb is coming out. Or
indeed do another test to assay something else, like Ba or V or
what-have-you. It may be possible to use the residue for further, not too
expensive, diagnostic tests, but it's really just there to give you an idea
of how durable the glaze is. I'm hoping to do some work on this, perhaps
this summer. In the mean time, I'd be interested in any and all comments.
Gavin
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