Is my glaze food safe?
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So you've created a great glaze, but how can you be sure it will be food safe after firing? Leaching occurs when metals diffuse through the fired surface and consequently contaminate food & drink.

Lead is a major concern. There have been many cases of poisoning & fatalities due to lead leaching from pottery. Acidic beverages or food like tomatoes or fruit juice and continual microwave heating are a problem. Ceramic ware can be tested for lead release, there are FDA guidelines that provide the maximum amount of lead that can leach and still be safe.

(See below site for detailed info on lead test kits & release data) http://artsnet.heinz.cmu.edu:70/0/csa/arthazards/visualarts/ceramics

Cadmium is the only metal besides lead currently regulated in the US & Canada. Test for release.

Barium can leach in certain formulations. Test.
(If a barium glaze or any glaze changes color from food contact, do not use it for food.) 

Use glazes with calcium, magnesium, potassium, & sodium fluxes & minimize the amounts of toxic metal colorants for glazes that will likely be food safe.

In all cases, test your glaze for metal leaching, contact your local pottery supplier for details.