Primary Test: Whether a blue faceted diffused sapphire or a surface diffused star sapphire, these should be an easy identification using magnification and an immersion cell. The faceted diffusion treated sapphire below shows the diagnostic color concentrations along the facet junctions. And star sapphire shows where the blue diffusion material concentrated along the surface reaching fissures causing color concentrations that are easily visible. Sapphires that are surface diffused will show these color concentrations that are diagnostic.
Secondary Tests: None needed.
Repair and Setting: Based on the diffusion treatment being surface diffusion only, no heat of any kind should be applied to this treated gemstone. Not recommended for any torch heating, nor for cleaning in ultrasonic as the stability of the surface diffusion may vary widely from stone to stone.