Lou, Polarization and cross-polarization, while sometimes unavoidable, present a whole stack of color reproduction problems, partly addressed in the other responses to your question. The reference Lab values for the profiling chart must be made under the same conditions as those present in the capture of the painting. If the painting has a matte surface this is greatly simplified, but in this case not only is the instrument filtering and illuminant angle, etc, (assuming you are measuring the chart yourself to derive the ref values) are not the same as in your shooting setup, but the target is itself nothing like the painting, either in the spectral signature of its colorants (including possible fluorescing of the paints) or, more importantly, in its surface: A rough, glossy-surfaced painting will not correspond with spectrophotometer contact measurements made of a matte-surfaced target--not even close--even if you use an instrument with a polarizing filter. There may also be issues with the response of the DSLR chip to polarized light, as when a polarizing filter is placed over the taking lens. I doubt there is much you can do beyond profiling conventionally (preferably measuring with with a polarizing filter) and doing the rest of the correction manually in Photoshop. Those skills are still important! Mike