By Timothy A. Mouw - X-Rite Incorporated
There has long been a debate over the proper type of instrument (spectrophotometer) geometry to use when measuring metallic inks. These inks typically contain aluminum flake pigments, either as a separate layer which is overprinted with a colored ink layer, or as an ingredient within the colored ink. In either case, they produce a very desirable appearance, exhibiting a shift in color (known as color travel) dependent upon viewing angle. While these color shifts are visually appealing, they can be challenging to characterize properly.
When choosing an instrument to be used for measuring these inks there are several things which must be considered. Perhaps the most important thing to be considered is the geometry of the instrument, which will greatly affect the outcome of the measurement. Instrument geometry is described.