Thanks for the contributions thus far.

Do studio potters in California test their work? Would it be
only pieces with say Cobalt in the glaze, one piece per batch?

I find a there's a lot of truth and rumour about glaze safety.
I don't know if many studio potters test at all and how
many of those test with other than simple kits. I know some who
take a glaze from the glaze book mentioned above, a glaze with cobalt,
noted with a low leaching rate and then consider the glaze safe even
when a differant feldspar is used. I've known some who used
lemon juice to visually check for leaching.

I do find that potters are in some ways expected to have higher
standards than plastics. Now there is a big variance in
concern and knowledge about glazes. I know some ( one ) who are very
concerned about crazing and test pieces with repeated heating and
freezing. There is concern over crazing even if no toxic
materials are imvolved, as bacteria could grow in the cracks.
That's a lot of concern considering that many/most people store
food in plastic that is easily scratched and there's little
concern about build up of bacteria there. I've also noticed some
plastic companies warning about heating food in plastic storage
containers. But it's widely done and I havn't seen a recall of
plastic containers. Let's face it, if overheated the plastics
melt down. They are created by huge companies and the studio
potters are very small. Of course, a single potter is a lot
easier to sue than a big petrochemical corporation.

Do any of you know of rules of thumb for glazes e.g.: no more
than 5%, 3% copper; no more than 1% cobalt; toxic material
okay if under clear glaze. Do you know of any glaze myths?

Do you have categories of food safe such as: table safe, safe
for dry foods only, microwave safe, safe for storage of acid
items like salads?

( Safety for oven or microwave concerns the clay body as much or
more than the glaze.)

Are the big manufacturers of "good china" still using lead glazes?
( in factory conditions with safety confirmed by testing )

Still curious and welcoming imput,

Elaine