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Thursday, February 27, 2014

How do we establish a master color/brightness standard?

Most mills today produce a variety of grades e.g. shades, weights and sizes. Also, companies want to be able to produce the same grade at any of their mills based on demand. They want the flexibility to move production of a certain grade to any of their mills based on customer needs, production efficiencies and utilization rates.  One thing that is necessary in order to make this work is to have a master color/brightness standard which all mills can produce to.

The master standard should always be established from one "originating" mill and one "originating" machine at that mill.  If at all possible, this machine should be the machine that produces the largest percentage of this grade for the market.  Once the master standard has been established, a large sample should be sent to all the mills for establishing their master file, master sample and reference sample (this will be covered in a future post).


Black bag and master samples
The master samples should be kept in a light-proof container, typically a sealed, heavy duty, black, plastic bag.  The master samples should be kept in a freezer to insure a longer shelf life.  The master samples should be checked on the originating mill's spectrophotometer at least once every few months to insure the master sample has not changed or degraded over time.  The master sample must be opened to atmosphere and allowed to acclimatize to lab conditions for 24 hours before being measured. When the first signs of degradation are detected in the measurements, a new master sample has to be established.  Acceptable limits are to be established for this degradation measurement.

When replacement of the master standard becomes necessary, the new master standard should come from the same mill and the same machine.  This master standard must be a good non-metameric match (reference Metamerism posts).  If major changes occur to the machine e.g. a top wire former is added, a new master standard may need to be established as soon as the changes on the machine have been stabilized.

Also, if any major changes in the mix of species (HW, SW, recycled) is made, a new master standard must be established.  Finally, if any change is made to the dye being used (supplier, type, mix) a new master standard will most likely need to be established.

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