Interlaboratory comparison and validity study of the Minolta ChromaMeters CR-200 and CR-300

Interlaboratory comparison and validity study of the Minolta ChromaMeters. The aim was to study repeatability, day-to-day variation, week-to-week variation, effects of electrical switch on/off, different pressures used and external light conditions.

A circulation experiment among 4 European laboratories using the same procedures and measurements on the same circulated colour standards (white, pink, red) and on forearm skin. Measurements using both the laboratories actual in-house calibration setting and calibration of all apparatus against a common white standard tile were performed.

High instrument repeatability for all apparatus with low coefficients of variation was found. The repeatability was poorer in vivo on forearm skin than on colour plates. Interday reproducibility was found to be high. One apparatus showed an unexpected major shift in a* and b* levels, probably related to the device. Interlaboratory calibration against a common white tile was found inadequate, since a large inter-individual variation will always be present and will exceed the instrument variability, and since a difference in measuring level among devices could not be overcome. Increased pressure of the probe during forearm skin measurement introduced increased a* values. When doing more than 3 replicative measurements within a test site, the equipment should always be removed between each measurement, since continuous contact may result in larger in vivo variability. No effect was found of turning the electrical power on/off. Neither was ambient light found to influence the measurements. The use of a glass projection tube instead of the normal open tube was found to influence a* by decreasing the value.