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Proofing if utensil is 'microwaveable' ?

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Advanced Member level 2
Jan 29, 2004
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Daily, for decades, I warm up my breakfast beverage with the teaspoon left in the cup, all fine, always. Never a knife or fork goes into the microwave oven. Spoons are OK. Few people knows this.

How to test if another metal utensil will not create sparks or damage the appliance ? It will be a 10 cm long hollow square 4mm x 4mm internal, 5mm x 5mm external; brass, bronze, iron, copper, aluminium if it matters. Do I test such together with other item like a glass of water or can risk-testing by itself ? What does the theory says ? The plastic one I made deforms with the heat :sneaky:


Maybe no damage happen if you put the teaspoon in the cup, but I think the efficiency of the microwave heating system will decrease dramatically.
Perhaps you need at least twice the time to heat the liquid with teaspoon inside compared with teaspoon outside. There are no reasons to place any metal inside of the microwave ovens.
I think you are the only person that can answer to your question, placing different metals inside of a microwave oven. Do the test and let us know...or call 911 :)

Spoons are OK. Few people knows this
Geometry matters a lot; the induced eddy currents acts likewise the static electricity, electrons mutually repulse each other at the surface of the metal, and the thinest tip, the greatest electrical charge density, the highest electric field gradient. So, being the spoons in rounded shapes, although not evincing so dramatically the sparks, doesn't means that there is not eddy currents there; Perhaps, also due most part of this utensil is submerged on the water, part of the energy get damped there.

Also, you say the spoon was inside the tea/coffee. I would say that the water absorbed the EM waves and was much attenuated when they reached the spoon surface.
The theory says if the material's conductivity is high, don't put it in a microwave.

Spoons are OK. Few people knows this.

In my opinion, this depends on physicals dimensions compared to wavelength (2.4 GHz => 125mm). If your metal object length is a multiple of lambda/2 (62.5mm) it will short circuit the local RF fields.

Edit: the calculation above is for a piece of metal in air. When immersed in water (large permittivity) it becomes even more complicated. I'm glad your spoon experiment worked for you, but it's not safe in general.

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