https://en.wikipedia.org/wiki/Kirchhoff%27s_law_of_thermal_radiation
Basically. an object cannot radiate more or less heat than it absorbs.
Quoting your wiki link:
it had been experimentally established that a good absorber is a good emitter, and a poor absorber is a poor emitter. Naturally, a good reflector must be a poor absorber. This is why, for example, lightweight emergency thermal blankets are based on reflective metallic coatings: they lose little heat by radiation.
There's nothing contradictory there. It means that a body cannot emit more or less than it absorbs. An object with low absorption will heat up less in the same time as an object with high absorption, and correspondingly the less absorptive material will radiate less energy than the more absorptive material.
Precisely! And that's why the shiny steel ball doesn't glow bright orange like the rusty ball.
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