Identifying a rough ruby is difficult to differentiate from rubillite, red spinel, tourmaline, garnet, and even harder from pink sapphire, generally accepted by professional gemologists to be simply a lighter, pinker version of the same stone. Thus, the determination between ruby and other red gems turns on colour. As colour is the visual interpretation of a specific point along the light spectrum, the easiest way to identify ruby is with a dichroscope, an instrument that looks like a longer version of a jeweller's loupe and uses internal prisms to separate light into its individual vibrational directions as caused by its passing through the stone. Once the light frequencies are clearly separated,` it becomes easy to identify the bi-tonal, or dichroic, signature of a ruby.
Hold the rough stone directly in front of a white light source so the light shines through the rough stone.
Touch the lens of the dichroscope to the stone, and look through the eye piece.
Note how many squares of colour are presented inside the dichroscope. Ruby is dichroic, which means its structure causes light passing through it to break down into two separate vibrational frequencies. Thus, if the rough stone is a ruby, the viewer sees two colour squares inside the dichroscope. The colours must be purple-red and orange-red.
Keep the eye to the dichroscope eye piece and slowly rotate it between the fingers, as one would a kaleidoscope, and watch the colour squares inside the instrument until the colour squares are back in their original position. If the purple-red and orange-red squares are both present through the dichroscope's entire rotation, further verification is presented that the stone is dichroic, which indicates ruby, and that those two colours are a true purple-red and an orange-red, also indicating ruby.
Rotate the stone in front of the light while keeping the dichroscope stationary and observe the colour squares inside the instrument. Repeat the observation of the stone from four additional different angles, for a total of five different points of viewing, all the while observing the colour squares inside the instrument.
Identify the stone with confidence as ruby if two colour squares are consistently observed inside the dichroscope from all five different viewing points, and those two colour squares are always purple-red and orange-red.
Do not use fluorescent light as the light source behind the stone when using a dichroscope as fluorescent light often produces false readings within the instrument.