It is an essential device in identifying colored stones. While it was originally intended to rapidly differentiate between genuine Rubies and the pastes and doublets which resemble them it also is a valuable aid in identifying other colored stones as well. Designed to transmit only deep red and yellow-green light and the best results are obtained when stones are examined under a strong electric light. Ruby Filter is definitely a helpful tool in identifying certain red blue and green stones. With Ruby filters, you can differentiate the genuine rubies from the fake once as well as checking the authenticity of sapphires with comfort and ease.