Source: Begemann B., Dorschner J., Henning Th., Mutschke H., and Thamm E. (1994) A laboratory approach to the interstellar sulfide problem.
Astrophys. J., v. 423, pp. L71 - L74.
Some details:
The sulfides were synthesized from the native elements
by the evacuated silica tube method with an annealing at 1273 K.
The resulting sulfide powders were portioned, pressed to pellets,
and melted in an arc furnace. The molten samples were quenched.
 
For samples with x=0.0, 0.1, 0.25, 0.4, 0.5, 0.6, 0.75, 0.9,
reflectance by polished surfaces was measured in the range
from 2 to 500 microns. The refractive index was determined
by Kramers-Kronig analysis.