Comment by irjustin

> Might be, but those shock diamonds are not a great sign for their nozzles despite being beautiful

Shock diamonds do not determine nozzle health/stability. The diamonds themselves are 100% part of nominal operation.

What you're looking for is flow separation from the nozzle because it's under expanded leading possible instability. Scott Manly did a great bit on it[0].

[0] https://youtu.be/l5l3CHWoHSI?t=261