Gemstone is a kind of sample with special physical appearance. Are there any test methods or instruments recommended for the following situations?
1. Testing gemstone samples with high transparency, small size and strong surface luster
2. We want to study the color change of gemstones under different light sources and illuminations.
3. Some optical effects related to light, such as opal's schiller, Labradorescence, etc.
Dear Guo Ying,
In general your gems will reflect light either diffusely or in a specular (directionally beamed) manner. In transparent materials the colour of the surface reflectance may also be different from that from the body of the object. Lustre and related phenomena occur when the reflection is a mixture of both specular and diffuse modes. Instruments that measure both the intensity and direction of reflectance are known as a ‘Goniometers’ .The ultimate instrument is a ‘Gonio-spectrophotometer’. Such instruments carry out a spectral content analysis of the reflected light in addition to intensity and specular angle measurement. Commonly, a 3D hemispherical map of overall reflectance is generated.
Small sample size is typically resolved by placing the object against a small aperture in a diffuse reflectance sphere which eliminates stray light. The relevant illuminant and measuring sensor likewise each have a dedicated access port .Given an appropriate practical setup such instruments would be able to meet all three of your requirements.
Dear David Oulton ，Thank you for your advice. We are currently using an X-Rite spectrophotometer, which has only one light source inside, and can convert the test results into data of different light sources through an algorithm. Is there any other product that can change the real light source to obtain the actual measurement data?
Thanks again
Dear Guo,
It is not necessary to change the light source. it is only an enabling feature of any given colorimetric analysis and in general it only needs to provide a stable, smooth and comprehensive spectral profile. It is entirely valid to use full spectrum illumination of this type in order to predict the effect of alternative illuminants such as D65 artificial daylight. However the effect of line element spectra (as in fluorescent tube light) cannot be predicted.
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