Instrumental evaluations, like visual evaluations, must be accurate, precise and reproducible. The reproducibility issue with instrumental evaluations can be a hidden problem. When generating numerical and/or graphical data for colored samples, reproducible data becomes a statistical issue.

Often, users will measure a sample once, then use that numerical reading as an absolute and indisputable reference. Such practices are risky, and observers should perform statistical Gage Repeatability and Reproducibility studies (GR&Rs) to determine the number of measurements that must be averaged to generate acceptable data. ColorXpress™ Services has conducted Six Sigma GR&Rs which have indicated that a minimum of 2 measurements (ideally with 90° rotation) should be averaged for acceptable measurement system variation.

Most of the objectives of a numerical instrumental assessment are similar to those of a visual assessment. All must be satisfied to generate valid data. This is the reason that ColorXpress™ Services asks for the measurement criteria on our Color Match Request form.

The Instrument and Data Evaluations:

• Sample viewing surfaces must be specified.
• Identify instrument used to generate color data.
• Determine transparency, translucency or opacity of the sample(s).
• If the sample(s) are not instrumentally opaque, specify how the measurements should be accomplished (transmission mode or reflectance mode, specify surface used to back up the sample).
• Specify measurement illuminant(s).
• Specify specular component included or excluded.
• Specify UV component included or excluded.
• Specify observer function utilized (2 degree versus 10 degree).
• Identify the specific data that will be generated and recorded.
• Colorimetric data (L*a*b*, L*c*h*, etc.).Colorimetric data (L*a*b*, L*c*h*, etc.).
• Reflectance curves.
• Communicate and agree upon all aspects of the assessment.




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