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Most operators set their vacuum oven to -29.9 inHg and 110F and walk away. The problem is that residual butane in a shatter slab forms a concentration gradient: the surface outgasses first, creates a skin layer with sub-50 ppm solvent, and traps everything underneath.

The fix is staged. First pull at -15 inHg and 90F for 2 hours to let butane migrate without ballooning. Then full vacuum at -29.9 inHg and 110F, with the oven cracked every 4 hours to replace the atmosphere. The nitrogen purge accelerates the concentration gradient because you are replacing butane-saturated headspace with clean gas.

Operators who skip the staging step and go straight to full vacuum spend 72 hours in the oven instead of 36. The shortcut doubles the cycle time.

Full solvent-specific purging SOPs:

How to Purge Residual Solvents from Cannabis Concentrates Butane purges differently than ethanol. Solvent-specific vacuum oven SOPs with temp ramps, pressure staging, state compliance limits, and mass-loss diagnostics.