Gloss (in Color iQC) applies to measurements made on a sphere instrument (where SPI and SPE are possible), and uses an equation (developed by X-Rite) that is correlated to a 60 degree gloss meter for paint samples on paper. It is generally close to an actual gloss meter within the normal ranges of 20-80 – but may different somewhat at the low or high ends of the range. Every spectrophotometer has a different form of the equation to account for differences in sphere size, number of holes, size of specular port, etc. We have supplied a general form of the equation, and specific forms for CE7000, Color i5/i7, XTH, and SP62/64. All other sphere spectros use the general form of the equation and do not agree as well. The ASTM method that applies to this is D523 – although the type of equipment required by D523 does NOT include sphere instruments – therefore the equation gives us a “correlated gloss” value rather than a “60 degree gloss” value.
SRR Gloss (in Color iQC) is “Specular Reflectance Ratio” and is defined as ASTM method E429. This method is titled “Measurement and Calculation of Reflecting Characteristics of Metallic Surfaces Using Integrating Sphere Instruments” , and in general is useful for describing the specular reflectance from surfaces that are somewhat glossy. An inverse value called “diffuse reflectance ratio” is normally calculated for comparing metallic surfaces which are matte (this DRR value is NOT contained in color iQC).
The methods will give similar relative comparative results between several samples – but the values themselves will be different.