# Meaning of red heat

I have two reactions below.

What is the difference between red heat and normal heat? Is it related to iron as a catalyst when it is red hot?

• Red heat is normal heat, quite a bit hotter than 473K. It is not related to iron in any way. – Ivan Neretin Jan 18 '19 at 13:42
• All black bodies (at least the ones that don't decompose when hot) emit essentially the same radiation. The colour of that is a good indicator of the temperature. Red heat is the temperature where things glow red whether they are glass or steel or some other inert substance. And that is pretty hot (as the answer says 500-600 °C). – matt_black Jan 18 '19 at 15:51
• I removed second question that was homework question. read carefully. – A.K. Jan 18 '19 at 23:55

## 1 Answer

We know that an object when heated upto a certain temperature emits radiation in form of light. This is called thermal radiation. The color of the radiation depends on the temperature and/or physical proerties of the object. The radiation obeys Wien's law. So, when said "red-hot", it means that the object is heated upto a certain temperature such that the object glows red.

After a quick Google search, I came across a reference that said "red-heat" is observed somewhere between 500-1000°C and is standardized somewhere at 555°C although this range varies according to property of object.

For a particular metal, range of red heat is:

$$\begin{array}{c|c} \mathbf{Color} & \mathbf{Temperature(°C)} \\\hline \text{Faint red } & \text{500}\\ \text{Blood Red} & \text{580} \\ \text{Dark Cherry } & \text{635}\\ \text{Medium Cherry } & \text{690}\\ \text{Cherry} & \text{745}\\ \text{Bright Cherry} & \text{790}\end{array}$$

• What do you mean by rubber? Rubber most certainly does not survive even the lowest of the mentioned temperatures. – Ivan Neretin Jan 18 '19 at 15:02
• @IvanNeretin Normal rubber melt at lower temperature(180 C) but rubber tires do melt at even higher temperature(600 C). But for the benefit of doubt, I am removing the data for rubber but no to say at least that the data came from rubber industry and thus I interpreted the object to be rubber. – Nilay Ghosh Jan 18 '19 at 15:18
• Thats the reason i asked red hot. How can crystals become red hot? Its why I thought of iron as a catalyst – Som V. Tambe Jan 18 '19 at 15:19
• Anything can become red hot, unless it decomposes before that. – Ivan Neretin Jan 18 '19 at 15:20