Opal can be divided into black Opal, white Opal, yellow Opal, etc. based on its color, with black Opal having the highest price. In order to elevate the quality of lower priced white or yellow opals, some people use manual methods to change their color and become "black opals" to seek high profits. The main method is to boil with sugar or inject plastic to make the white opal black. The method of identification is that the specific gravity of opal after sugar boiling or injection molding is significantly different, and when tested in water, its specific gravity value becomes lighter. Injection molded opal can also be tested using heated needles. Natural opal hot needles cannot penetrate, while injection molded opal can penetrate and produce a smell of plastic after closing.

Tourmaline is a mid range gemstone, but due to the high value of peach red and bright blue tourmalines, there are also counterfeit products appearing. There are two common types of counterfeit goods, one is artificially colored with colorless tourmaline; One is made of red glass processing. The method of recognition is that true tourmalines often have obvious dichroism, with visible double shadows; Tubular inclusions or wadding like substances can be seen inside the body, and the cross-section of the crystal is curved in a triangular shape. These characteristics are not possessed by counterfeit products. The tourmaline dyed by workers is not difficult to identify due to its stagnant color and the lack of natural tourmaline's "precious light".