Potassium mirror ?

Heating a question mark shaped retort tube which was welded on one end snd coupled with a 10mm borosilicate tube on the other end had a nice effect.
I heated K2CO3 + C to over 1200 C (probably more because the tube melted) and saw a nice mirror appearing on the glass tube. That must be condensed K metal, but was unable to capture it in the oil. Anyway, after cooling I dismantled it and saw the still nice mirrored tube connected to the (deceased) retort.




UPDATE: When it was cooled down I poured some water into the glass tube and indeed lilac flames appeared which was an indicator of the presence of K metal.

[Edited on 2023-8-16 by metalresearcher]