What causes 'hot spots' on some plates or cups when they are placed in a microwave oven?

Brisco County

Metal in the item, Glazing contains metals Jan 13 04, 1:11 PM

robboy

Thanks---any idea as to what percentage is allowed, considering those items advertise themselves as being 'microwave safe'? Jan 13 04, 6:35 PM

sequoianoir

I would suggest that the microwave oven you are referring to is not one that has a rotating turntable in the bottom (or a microwave stirrer elsewhere) If glazing does contains metals they should be evenly distributed and would not be the cause unless there was a glazing flaw which I believe would be visible. Also if it was a glaze fault then the position of these hot spots would always be in the same place for a specific plate and never "move around". I think the actual answer is down to two possibilities. If the EMPTY plate is not on a turntable (or no stirrer) then it is sitting in a fixed standing microwave field. These waves are sinewaves (with peaks and troughs) and generate maximum heating effect at these points. At the zero midpoint, the positive to negative crossover, no heat is generated at all. The other answer is based on the plate actually having food (of different sorts) on it. Different foods will heat up at different rates depending upon water content, fat content, density and other factors. Due to natural conduction the plate may get hot from the food with differring transfer rates depending upon the thermal contact properties and total area. Additionally those foods with a pierced skin where jets of steam burst out, like jacket potatoes, will heat a plate in one place and not another. Jan 14 04, 6:02 AM

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