Thread: Microwave Oven AND Porcelain Bowl

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

Originally Posted by wuchieh

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

No, unless it's a porcelain that contains metals as part of it's makeup. There are a few of those types but they are pretty rare today. Another situation is where the bowl (or plate) is completely covered with decorative paint that is metallic based.

But other than those two very unusual conditions, it's just urban legend.

Originally Posted by Old Geezer

Originally Posted by wuchieh

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

No, unless it's a porcelain that contains metals as part of it's makeup. There are a few of those types but they are pretty rare today. Another situation is where the bowl (or plate) is completely covered with decorative paint that is metallic based.

But other than those two very unusual conditions, it's just urban legend.

How about the part that says that blocking the microwave will still result in the food being cooked?

Originally Posted by wuchieh

Originally Posted by Old Geezer

Originally Posted by wuchieh

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

No, unless it's a porcelain that contains metals as part of it's makeup. There are a few of those types but they are pretty rare today. Another situation is where the bowl (or plate) is completely covered with decorative paint that is metallic based.

But other than those two very unusual conditions, it's just urban legend.

How about the part that says that blocking the microwave will still result in the food being cooked?

If they were completely blocked, no, it wouldn't cook. But keep in mind - even partially blocked microwaves will cause MUCH sparking and arcing inside your oven. You would know it the instant you turned it on. :wink:

Originally Posted by Old Geezer

Originally Posted by wuchieh

Originally Posted by Old Geezer

Originally Posted by wuchieh

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

No, unless it's a porcelain that contains metals as part of it's makeup. There are a few of those types but they are pretty rare today. Another situation is where the bowl (or plate) is completely covered with decorative paint that is metallic based.

But other than those two very unusual conditions, it's just urban legend.

How about the part that says that blocking the microwave will still result in the food being cooked?

If they were completely blocked, no, it wouldn't cook. But keep in mind - even partially blocked microwaves will cause MUCH sparking and arcing inside your oven. You would know it the instant you turned it on. :wink:

Ok, last question, I promise: given the two scenarios, which one is better in terms of microwave radiation exposure to the foods?

1. Partially blocked food (by covering it with porcelain bowl painted or mixed with metals) heated for a longer duration (this part seems natural given that the microwaves are partially blocked)

2. Exposed food cooked at a shorter duration but with full exposure

The more important point is this: will partially blocked food cooked at a longer duration result in MORE radiation exposure or less than compared to the fully exposed food cooked at a shorter duration?

Originally Posted by wuchieh

Originally Posted by Old Geezer

Originally Posted by wuchieh

Originally Posted by Old Geezer

Originally Posted by wuchieh

Question for you guys: I heard recently that if one were to cover a dish containing foods with a porcelain bowl and then heating it inside a microwave oven, then the bowl would block the microwave radiation from contacting the food, yet still leave the heating effect of the microwave, thereby heating the food all the same. Is this theory correct or simply a myth? It is my belief that in order for the oven to heat the intended foods, the microwave must actually contact the water particles inside, and if something were to block the microwave (and its radiation effects), then the food would not be heated. Furthermore, can a porcelain bowl actually block microwave?

No, unless it's a porcelain that contains metals as part of it's makeup. There are a few of those types but they are pretty rare today. Another situation is where the bowl (or plate) is completely covered with decorative paint that is metallic based.

But other than those two very unusual conditions, it's just urban legend.

How about the part that says that blocking the microwave will still result in the food being cooked?

If they were completely blocked, no, it wouldn't cook. But keep in mind - even partially blocked microwaves will cause MUCH sparking and arcing inside your oven. You would know it the instant you turned it on. :wink:

Ok, last question, I promise: given the two scenarios, which one is better in terms of microwave radiation exposure to the foods?

1. Partially blocked food (by covering it with porcelain bowl painted or mixed with metals) heated for a longer duration (this part seems natural given that the microwaves are partially blocked)

2. Exposed food cooked at a shorter duration but with full exposure

The more important point is this: will partially blocked food cooked at a longer duration result in MORE radiation exposure or less than compared to the fully exposed food cooked at a shorter duration?

Number 2 is by FAR the best. Partially blocked radiation is wasteful and cause nothing except a higher power bill and possible damage to the klystron or magnetron electron tube which generates the microwaves.

One thing that few ordinary people know is that the internal of the oven cooking space is a finely-tuned microwave cavity. It's dimensions are very carefully calculated and constructed to match the precise operating frequency of the oven. Anything that interferes with that has a negative impact on it's operation and service life. People often do silly things like placing aluminum foil in them to make them spark and then pull it out thinking they've hurt nothing. But they've shortened the life of their oven.

I don't mind questions at all, if you have more please feel free to ask. I spent many years working with microwave-generating devices, transmitters and receivers (in communications applications) and waveguides for carrying the microwaves. Since I've retired, I still keep up with the latest developments and designs but don't get to talk about it very often. :wink:

Surely putting any kind of metal in a microwave (like metallic paint) would make it go on fire? I've seen this happen.

Oh and also, puttting food in for a low heat for a long time or a high heat for a short time depends on the food.

For example, you wouldn't put a roast chicken in a 400 hundred degree oven for 5 mins, as it would burn, and you also wouldn't put an egg in a frying pan on 20 degrees for an hour, as nothing much would happen except you may have a smelly egg.

sounds too much like homework...

I have a few questions for you, Old Geezer.

What is the typical frequency of the klystron in a home microwave oven?

How much spread in frequencies is there?

When microwaves are directed at a food sample in the oven, how much energy is typically absorbed and how much lost or wasted?

Originally Posted by Hazz

Surely putting any kind of metal in a microwave (like metallic paint) would make it go on fire? I've seen this happen.

Certainly. That's why I said it will cause arcing and sparking. And if there's anything combustible present, that can result in flames.

Oh and also, puttting food in for a low heat for a long time or a high heat for a short time depends on the food.

For example, you wouldn't put a roast chicken in a 400 hundred degree oven for 5 mins, as it would burn, and you also wouldn't put an egg in a frying pan on 20 degrees for an hour, as nothing much would happen except you may have a smelly egg.

Of course, that's obvious. And that's why the ovens have a power setting (adjustable) as well as a timer. Some have a continuously variable power setting while others have presets like high, medium, low and defrost.

Originally Posted by SteveF

I have a few questions for you, Old Geezer.

What is the typical frequency of the klystron in a home microwave oven?

How much spread in frequencies is there?

When microwaves are directed at a food sample in the oven, how much energy is typically absorbed and how much lost or wasted?

Hello, Steve,

The most common standard frequency is 2450 MHz (or a wavelength of 12.24 centimeters). It was selected because of the dimensions of the cavity (oven cooking space) and so that small amounts of leakage would not present much of an interference problem with other commercial electronic devices.

There isn't any spread. It's a single-frequency, unmodulated carrier wave.

It's a very efficient system - well over 90%. The microwaves simply bounce around inside the cavity (oven) until they are absorbed by the food. The 'missing' part is generally absorbed by moisture-containing particles on the metal surfaces and humidity in the air.