Application of Surface Contact Angle and Surface Tension Measurements in the Identification of Gem Materials

Surface tension is one of the important physical and chemical parameters of the solid surface, which is closely related to temperature and properties of the phases between the boundaries. Based on the Young function, the contact angle measurement method to calculate the solid surface tension has been widely used in surface science and engineering Comparing to other solid materials with inhomogeneous surface, most gemstones have a smooth surface, making it easy to measure the contact angle. In this study, the contact angle of 15 different types of natural and synthetic gemstones including diamond, moissanite, CZ, tourmaline, topaz, jade, amber. And some coated gemstones and fissure filled gemstones have been measured and compared using a dynamic contact angle testing device (FTA200). It was found that the differences in the contact angle for different types of natural and synthetic gemstones are suitable to be used in gemstone identification. For example, contact angle value of diamond and CZ is 56.68° and 37.79°, respectively. Furthermore, the contact angle values between the gemstone and gems with coating process have significant differences, such as the contact angle value of amber is 92.49°, while coated amber is 66.49°. Due to the limitations of the droplet size control restricted by experimental conditions, the contact angle of the fissure-filled gemstones cannot be measured accurately. Herein, this method is not suitable to identify gemstones with artificial fillings. Research shows that contact angle and surface tension values can be used as the basis of supplementary identification of gem species, especially for coated gems. Compared with the conventional gem identification methods (e.g. Infrared Spectrum, the refractive index measurement), contact angle measurement method has higher measuring accuracy, simple operation without destroying the sample, and conforms to the basic principles of gemstone nondestructive identification, especially for high refractive index gem. Contact angle measurement can solve the detection problems for surface-coated gems and related surface property.