Measuring gloss on flat transparent materials such as glass and plastic can be problematic because light is reflected from the front surface and internally from the second surface
Transparent materials will reflect from the front and rear surfaces, resulting in higher gloss measurements than when measuring the top surface alone.
To measure reflection from the front surface only, light entering the material needs to be absorbed and not reflected from the second surface.
Matte black camera bags are less expensive and better absorb any light that passes through the material Any air between the clear material and the foil will cause the second surface to reflect light - a liquid is required to optically bond the clear material to the black foil .
To completely eliminate second surface reflections, a liquid with a similar refractive index to the test material should be chosen.
In fact, one drop of water or isopropanol (which evaporates after the measurement) is sufficient to obtain accurate gloss results for most clear samples.
