I have recently been doing some research into the working principle of a microwave kiln, and have run into a few things that continue to confound me. The first of which being that the devices evidently focus microwaves - which supposedly have a wavelength of ~12.2cm - through a tiny hole that is often no more than 1/2" in diameter, and achieve temperatures high enough to fuse glass. How can this be?

  • $\begingroup$ Do you mean "microwave ovens"? $\endgroup$
    – nasu
    Nov 9, 2020 at 6:53
  • $\begingroup$ Can you elaborate on what you consider the issue to be? Is it that the aperture is smaller than the wavelength of the microwaves? If so, what effect do you imagine that would have? $\endgroup$
    – J. Murray
    Nov 9, 2020 at 6:58
  • $\begingroup$ @J.Murray Yes, it is that the aperture is smaller than the wavelength of microwave radiation. I am not overly familiar with this area of physics, so I am not sure if it is as straightforward as "microwaves cannot fit through a hole smaller than their wavelength" or not. $\endgroup$
    – CJL
    Nov 10, 2020 at 19:18

1 Answer 1


Microwave kilns are made of a white insulating material. It is generally composed of a porous ceramic body with an inside coating of high temperature susceptor material. A susceptor material is the one which absorb microwave energy. Some of these can reach temperatures upto 1000 degree celcius. The actual composition of these materials are not known since they are patented trade secrets. The insulation of the kiln is the main reason of it reaching high temperature. The susceptor material also plays an important role.

The small hole helps it in increasing the temperature because once the microwave gets in it is a-kind-of-impossible to get out.

  • $\begingroup$ Thank you very much for that information, it makes a lot of sense now that I look at it again. So if I'm understanding this right, the microwaves enter through the hole, as well as through the susceptor material? I ask this because I am attempting to figure out a way to use this tremendous amount of heat to ionize the air inside of a specially designed chamber. $\endgroup$
    – CJL
    Dec 18, 2020 at 20:29
  • $\begingroup$ @CJL , this link might help you - google.com/amp/s/chatterglass.wordpress.com/2016/10/24/… $\endgroup$
    – lee
    Dec 28, 2020 at 15:17

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