MOTHER Feedback: Safety Regulations for Mexican Pottery and Combustible Gases

Eli P. Nielsen responds to two MOTHER EARTH NEWS NO. 31 articles about the need for safety regulations when using Mexican pottery and combustible gases.

| March/April 1975

  • Mexican pottery
    Don't mistake my intentions: MOM and her children have the right idea. It's just that I want all earth people to survive their own efforts toward self-sufficiency. 

  • Mexican pottery

Two "Dear Mother" letters in MOTHER EARTH NEWS NO. 31 prompt this city rat to write.

First, Bjo Trimble's advice on fixing lead glaze to make Mexican pottery "safe" for food handling kind of gives me the shakes. I'm no ceramic engineer, but I do know that most glazes — lead and non-lead — are actually thin layers of glass (or glasslike material, if you will). Such outer surfaces expand and contract at almost the same rate as the clay underneath and the almost is the part that gets you. Each time a vessel is heated and cooled, cracks form in the glaze. These are often microscopic and hence invisible but there can be miles (yes, literally 5,280 feet X ?) of such tiny fissures in one bean baker. This maze of cracks provides an enormous surface area that allows food acids to etch into the glaze and leach out the lead (cadmium, arsenic, etc . all good ceramics colors) into soluble toxic unplanned "food additives".

According to Bjo, the braceros taught her to bake the pottery in grease first, then boil it in vinegar. At the risk of sounding brutal, I wonder whether anybody has checked the average life span of braceros lately. It's miserably short and maybe mistaken "grandma" lore about lead-fired cookware causes as many deaths as short-handled hoes and pesticides.

A little knowledge of physics and chemistry suggests a possible modification of Bjo's process. First heat and cool your empty, dry bean pot rapidly several (6 to 10) times say by shifting it from a hot oven into cool, moving air and back. This ages and cracks the glaze without busting the pot. Then boil the crock with vinegar, but keep adding water so that the whole inside is treated. The acid will etch out all the fissures and remove the most soluble toxic salts. The next step is a further boiling with pure (distilled if possible) water — again with the vessel's entire surface covered — to remove more of the dangerous material. Finally, coat the pot's interior with corn oil, Crisco, or whatever. The grease, applied to a warm, dry, boiled-out pot, should soak into the cracks as if into a lamp wick. Since lead salts and the like don't dissolve in oil worth a darn, the resulting film acts as a barrier to keep food liquids (which are mostly water) from picking up too much contamination.

Warning: Don't bake in such ware treated or not. Cook in Pyrex or the like, and serve in the colorful, cute dishes if you must. Why? Because, if you heat the vessel long enough, more miles of cracks will open and expose more lead, etc. If you don't believe me, just ask any chemical engineer how to dissolve a solid. Somewhere in the course of his answer he'll tell you to "break the material up fine" — that's the cracks in the glaze and "apply heat in the presence of a solvent" in this case, the food cooking in that pretty, deadly pot.

I guess though I'm not sure that pottery treated as I've suggested and used for serving (not cooking) shouldn't pose too much of a toxicity hazard. Me, I'll stick to Pyrex!

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