Water, usually cold, is circulated in cold finger to allow the desired compound to be deposited.
1 Cooling water in 2 Cooling water out 3 Vacuum/gas line 4 Sublimation chamber 5 Sublimed compound 6 Crude material 7 External heating

Sublimation is the process by which a solid transforms into a gas without passing through the liquid stage. At normal atmospheric pressure, only some compounds like 'dry ice' (solid carbon dioxide) can go through this process. Most objects need low pressure in their surroundings to go through sublimation. There is low pressure in space.