What you are looking for are —dark vertical lines or fuzzy blocks where light is missing from the rainbow. Best Gemstone Tool (Spectroscope)
: Often produce a brighter spectrum, which is helpful for darker or more opaque stones. gem spectroscope
When starting out, you generally choose between two technologies, each with its own perks. What you are looking for are —dark vertical
: These use a series of prisms to refract light. you generally choose between two technologies