What happens if you heat an empty test tube over a Bunsen burner

What happens to the bottom of the test tube if you heat it on the yellow flame for 10 seconds?
If you then heat it on the blue flame, what happens to the bottom of the test tube now?

I think when heating the bottom of a test tube with a yellow flame for 10 seconds, some carbon (a black, powdery substance) would form since the flame is burning CO2. Because the flame uses up the oxygen, it basically takes it away from the CO2, leaving only C, or carbon.

When heating it with a blue flame, my guess would be that most of the bottom of the test tube would be covered with a lot of carbon, since a hotter flame uses up more oxygen.

You will get soot on the bottom of a test tube when you heat it in a yellow flame, since the gas in the burner is oxygen starved. The soot is carbon.

Heating it in a blue flame means there is sufficient oxygen to give a hot flame. The glass may glow yellow as it gets hotter. If not Pyrex, the tube may soften.