Is the instability surfical?
If so, I wonder if an inert gas might arrest decomposition.
This is that sample but after it was in the vac chamber for a while. Air bubbles got trapped when it was put into the Petri dish.
I just pulled it out now to dab and noticed that a big bubble that was there before had popped and was gone. In its place is a red ring of the red that appears when THC is in contact with the air. I believe it to be CBN.
That ring is centered in this photo over the upper left green corner of the silicon mat. It even makes a faint shadow on the work bench. This is just since late yesterday.
Just the air in trapped bubbles will change this stuff. I have a bell chamber vacuum chamber and will do a better purge next time because it pulls down way deeper.