24
Non-homogenous samples
Any sample which has mechanical structure or reflects differently at different angles
should always be averaged over orientation. This means that the sample (or instrument)
should be rotated between measurements. You should examine the sample by eye and
determine the nature of the structure. Cloth normally has threads at right angles. Some
worked or finished metal material may have structure in one direction. You should
determine a number of averages and amount of rotation which will give repeatable
results, and always use the same measurement procedure. The averaging procedure is
discussed in a later section of the manual. The default number of averages is set to three.
This default was chosen because three measurements with a one hundred twenty degree
rotation between each measurement often works well for averaging samples with
structure.
Problem samples
Samples which appear unusually bright may contain fluorescence. In some cases the
instrument will be able to make repeatable measurements on this type of sample, but
most matching and instrument-to-instrument calculations will fail.
Samples which change appearance as a function of point of view may contain metallic,
flake, or pearlescent colorants. In some cases, the instrument will be able to make
repeatable measurements on this type of sample, but most matching and instrument-to-
instrument calculations will fail.
