Graywolf said:

Shatter is carboxylic acid. It starts out that way, and softens through processing.

If the starting material is still young, we reliably get shatter by purging at 115F and -29.5" Hg until the solvent bubbles stop.

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Shatter is most definitely NOT all carboxylic acid! The THC-a is a pure carboxylic acid, but THC is an alcohol. What we know colloquially as "Shatter" is a combination of solids (THC/CBD and their cannabinoid cousins) PLUS terpenes, which are OILS at room temperature. Soft, flowing oils...
Add some oil to a solid and, if the solid is soluble in that oil (terpenes DO dissolve cannabinoids), then the solid will soften. It's that simple. Want rock hard shatter, then select high-thc strains...

Would anyone know y when I purge at -29.5 with the air release open up abit to maintain that exact pressure why my pump smokes oil abit out of the top where I put the oil? And it don't smoke when I close the air valve and bring the vac to max hg wich is around -31.5 hg / -32 hg around there?