Corundum (Lattice-Diffused) Classification
Lattice Diffusion Treated Corundum
Light To Dark Violet, Bluish Violet, Pure Blue To Strongly Greenish Blue, Purple To Pink, Reddish Purple To Purplish Red, Orangy Red To Red, Very Saturated Pink-Orange, Orange,Yellow
magnification with immersion, maybe fluorescence, higher than expected RI and pleochroism. For stones treated with beryllium you might have to use immersion with methylene iodide and maybe mineral oil. A blue filter is helpful when trying to detect faint color zoning in yellow to orange stones.
Stones can have an over the limit RI if treated with cobalt or chromium. Some stones might appear orange because the red layer polished of to reveal yellow core.