[Stoves] radiant heat capture, total heat measurement

[Richard Stanley]

Kevin & Frank:
 
Can I add my own experience with heating coffee  in our microwave ?: Certain iron rich clay cups will get hot as heck with luke warm coffee inside, while the other more "pure"  clays and glass cups don't --while their contained coffee rises to near boil in 30 odd seconds. U wave bands are admittedly  not in the IR band widths but it seems to offer a certain parallel here, in the discussion of emissivity/ reflectance, or no ? 
Richard Stanley