Ivor and Olive Lewis on fri 24 feb 06
Had a look through the pages of Paul Rado ("An Introduction to the =
Technology of Pottery" 1988. ISBN 0-08-034930-7) this morning:-
Page 209, 4. Behaviour under Microwave. "Microwaves pass through pottery =
without affecting it in any way .It is therefore a suitable vessel =
material for cooking in microwave ovens in which it suffers no thermal =
stress. Bone china, like other dense pottery, can thus be placed in =
microwave ovens. Porous (unglazed ) pottery is not recommended for =
microwave cooking...." Well, I checked on our two favourite mugs this =
morning since it was a "Coffee Day". Both half full of milk. One white =
porcelain, one a dark stoneware . Power on "High" for 1 min 40 secs. Top =
half of each cold/cool to the touch. Lower half of both hot from =
conduction of heat.
Must say, it is difficult to find anything other than the most =
elementary and generalised statements about the interaction between =
microwave radiation and material of any configuration though some people =
have done wonderful things to object they place in a microwave oven.
Popular explanation for microwave heating is that the microwaves cause =
water molecules which are polarised by their negative oxygen ion and =
their positive Hydrogen ions to rotate. Friction between rotating water =
molecules generates heat. Another one is that the bond between Hydrogen =
atoms and the oxygen atoms which has an angle of about 105 deg (rot) =
begins to flex and this causes friction.
Metal, I read during my search, can be melted in a domestic microwave. =
(Best utensil for that is a Silicon Carbide Crucible which can get red =
hot and contains no metallic elements. Insulate the crucible well with =
IFB or CF. Have a Water Ballast to mop up spare microwaves and prevent =
damaging the Magnetron Wave Generator.)
Silicon and Carbon have two unpaired electrons per atom. Iron has four =
unpaired electrons per atom, Cobalt three and nickel two which accounts =
for their prominent magnetic behaviour. The electron in Hydrogen atoms =
is (almost by definition), unpaired. Unpaired Electrons are responsible =
for the magnetic behaviour of some elements, their mixtures and =
compounds. Anything with magnetic properties is strongly influenced by =
electricity in motion be the current propagated via conductor or through =
space. I think this may be where the answer to the effects of microwaves =
on clay bodies and glazes may lay.
Best regards,
Ivor Lewis.
Redhill,
South Australia.
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