The fireproof sting turns black, what's the problem?

Question

Soldering

Bought a soldering iron. Set a low temperature (250 degrees). It was necessary to solder for a long time, so, while the soldering iron was lying on the stand, it turned black, and not only the sting, but also higher, at first everything was covered with a yellowish color, and then it began to blacken. For personal reasons, I think that this is either from rosin, or the soldering iron itself is defective. Here is a photo of the sting, this blackness is not rubbed off with a sponge or a fingernail.

Answer 1

What an impatient you are ...
I don’t see any problems - the working area of ​​\u200b\u200bthe sting is in order.