A really cool idea that probably won't work.

Saphire is really tough, hard and transparent. The
colors usually seen are contaminants.

On earth we drop Al O2 thru an H2 O2 flame, where it
deposits on a boule. The extreme pressure generated by
transition from a liquid phase to solid forces the
molecular structure into its lowest energy state, ie,
into crystaline saphire. Don't know how vacuum
deposition would work.
Might be interesting to try,,,

GAry 7