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For
a ceramic piece to be "foodsafe," all surfaces that
come into direct contact with food or drink must have smooth,
unbroken glassy surfaces, without cracks, rough spots of texturing
that water, juices or oils could penetrate. Such flaws can be
havens for bacterial growth.
- It
is not uncommon, however, to see bands of unglazed clay on the outsides
of handmade mugs, or unglazed rings at the bottom of plates and bowls.
These bands do not compromise the ware's foodsafe status.
- Do
unglazed areas on your ware come in contact with food or drink? For
pieces made from lowfire clays, any surface that comes in contact
with food or drink must be covered with a foodsafe glaze that has
been correctly fired in order to be considered foodsafe. Even when
fired, lowfire clay remains porous enough that fluids may penetrate
the surface and soak into the clay. Unglazed surfaces of pieces made
from midrange (stoneware) and highfire clays may be considered
foodsafe when fired to their full maturity because the clay particles
vitrify enough -- they melt together enough -- to form a waterproof
surface.
- To
be foodsafe according to US government standards, the glazed surface
must consist of less than 3% metallic compounds (copper, cobalt, etc)
which might leach into food or drink. This is especially important
for mugs or cups that might be used for acidic liquids like orange
juice or coffee. Some lead-bearing glazes can meet this standard when
fired correctly, but that's difficult to verify when buying finished
ware. It's simpler to avoid pieces glazed with lead-bearing products.
- If
you observe that any glaze on your piece changes color during or after
contact with food or drink, do not eat or drink from the piece.
- Raku
glazes are never foodsafe, even if fired in electric kilns, because
of their high metal content. Raku glazes are also rarely watertight.
- Some
pieces that meet the glaze standards may still not really be safe
for use because of hollows, pits or holes in the clay itself, under
the glaze. It's not uncommon to find small depressions inside moldcast
mugs where the handle meets the body, or holes in the clay at the
bottom of plates where the clay was poured into the mold. These holes
may -- or may not -- have been filled and sealed by the glaze. You'll
need to take extra care in cleaning these flawed pieces if you choose
to buy them. We've heard some real horror stories about what people
have eventually found in (or coming out of) these flaws.
- Ceramic
pieces with gold, platinum, or other "pure metal" decorations
are almost never microwave-safe.
- Some
ceramic pieces are microwave-safe, and some are not. It depends on
the amount and type of metals used in the clay and glaze, and the
power of your microwave oven. The only way to be sure is to test each
piece in the microwave. Fill it with water and zap it for 30 seconds
at a time. Watch for sparks from the ceramic piece -- a clear indication
there's too much iron! Handling the piece carefully, check for hot
spots and to see how much the clay has heated up. If you find uneven
hot spots, or the piece as a whole seems excessively hot compared
to the water inside, it's not microwaveable.
- Don't
put cool ceramic pieces into hot ovens. Put the filled dish into the
oven, turn the oven on, and allow about 10 minutes extra baking time
compared to the recipe instructions. Allow the ceramic piece to heat
up with the oven to minimize the risk of breakage.
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