Glazes and Decorations on Dishes
Information from the Food and Drug Administration
(FDA):
FDA has compiled the following information on
toxicity of dinnerware for Public Health Service's (PHS)
FDA Drug Bulletin (Sept.-Oct. 1977).
Glazes (compound glass coatings) are used to seal
the surface of dinnerware to make it shiny and smooth,
easier to clean, more resistant to wear, and less likely
to absorb organic matter and entrap microorganisms on
the surface. Decals containing heavy metals are often
bonded over the glaze, by firing, as decorations. Some of
these are more resistant than others and their rate of
release of toxic metals in the presence of acidic foods
varies greatly. When glazes and decals are properly
formulated, applied, and fired, however, no hazard exists
under normal use conditions in the absence of acidic
foods.
According to FDA, the most prevalent problem arises
from heavy metals in the decals and glazes, not only on
inexpensive pottery and intermediate-priced earthenware,
but also on expensive fine bone china. Under normal
conditions of use no health hazard is present, but
leaching of heavy metals (cadmium, lead) may occur when
acidic foods (carbonated beverages; cider; foods
containing vinegar; fruit juice, cooked fruits and other
fruit products; sauerkraut; tomatoes; wines, etc.) are
stored in dinnerware. Frequency of use, duration of
storage, temperature, and location of decals influence
the degree of toxicity produced. Decorative border decals
on flat dinnerware obviously pose much less of a problem
than decals on the inside bottom of a bowl in direct
contact with foods.
In 1970, FDA initiated a testing program for
imported dinnerware. In the early stages of the program
well known brands including even fine bone china were
found to be in violation of FDA guidelines.
In 1971, FDA began an inspection program to ensure
the safety of domestic dinnerware as well. Fortunately,
through government and industry cooperation the problem
has greatly diminished. FDA does, however, maintain
surveillance. If you purchase handmade pottery, ask what
is in the decals and glazes; be cautious about using for
acid foods listed above.