Elaine Stutt wrote:
I know we're not too active here but i'd be interested in your
definition of food safe and how you determine if a glaze or particular
piece of pottery is food safe. Anyone reading this in the next month
or so feel free to chime in.

Thanks,

Elaine

There are certainly legal standards set in both the European Union and
the USA which require tableware to pass extraction tests for both lead
and cadmium. I'm only familar with the EU position, and it's possible
that USA may also cover other elements.

The tests are based on the use of 4% acetic acid as the extraction
medium - the exact method to be used will be laid down in an EN or ASTM
standard, which will lay down the sample preparation, quantity of acid
to be used in terms of the type and volume / surface area of the plate /
bowl etc, as well as the extraction time and temperature.

Levels of heavy metals which have been extracted from the article into
the acetic acid are then determined using a suitably-sensitive analysis
method - general atomic absorption spectrophotometry or I|CP and the
result expressed generally in mg/litre or converted to mg/dm2 of surface
area. These can them be compared with the relevant legal limit.

As you can see, it's quite complicated and certainly not something which
can be carried out without a proper laboratory.

I have seen information on "spot test" kits which are sold in America
which rely on a colourimetric reaction of heavy metals with a
compplicated organic reagent normally known as dithizone. I very much
doubt the reliability of these test kits, as dithizone gives colours
with many heavy metals and other common ions block the colour formation.

Of course, if you intend to take this matter further, you should become
fully familiar with all the relevant legal requirements - for instance,
I believe that California has specific extra (different ?) requirements
as a result of Proposition 65.

Regards,

Phil