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Monday, March 3, 2014

How do you establish a Master Standard & Reference Standard at different locations?

Once the Master Standard has been established in the originating mill, samples should be sent immediately to the other mills making the same grade.  These other mills then are to read this Master Sample from the originating mill on their measuring instrument, and establish the standard data for the Master Sample.  The color measurement system numbers (e.g. L*a*b*) with a specific Illuminant/Observer condition (e.g. D65/10°) and UV Level (UV-EX, C, D65) that are chosen as the standard by the mills should also be recorded at this time.

Each of the non-originating mills now has to establish their own Reference Standard made on their own machine with their process variables.  The Reference Standard has to be an acceptable match to the Master Standard visually and with the chosen color measurement system on a properly calibrated, standard instrument by all interested parties.  It may be necessary to have different technical directors, the sales technical support people, and even key customers approve these Reference Standards and how they relate to the Master Standard.

Once the Reference Standard is established in each of the non-originating mills, this becomes the standard for that non-originating mill to use for judging if they have a match for future runs of that grade. Preservation of the Reference Standard samples should be done in the same way as the Master Standard samples.

Note: Why perform this step of establishing a mill specific Reference Standard? Color matching problems of this type have several problems, but one of the most difficult is separating two issues:
  1. The problem of matching any outside standard from another mill with different processes and different additives.  This is the most difficult match and if done with this procedure only has to be done once.
  2. The problem of matching any internal standard from your own mill from one day to the next, one month to the next, or one year to the next.
By separating these two issues, future standards matching in each mill becomes more manageable.

For more information on practical aspects of paper color matching, contact me at toddp@technidyne.com.