Skull Piston Shift Knob

I printed out my skull piston 3d model to use it as a shift knob and it's in progress.

Skull Piston in ZBrush

SLA Print (Liquid Resin) - Fail-

FDM Print with normal resin casting -Fail- Air bouble on the surface

FDM Print -Fail- Air bouble on the surface

FDM Print. Normal resin casting. Putty.

FDM Print. Pressure pot casting.