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Monday, October 27, 2014

A Story from the Testing Lab: What is 100% on the TAPPI Brightness Scale?

The first paper brightness tester utilizing directional geometry, the GE Reflection Meter, was developed and introduced to the Pulp and Paper Industry in the early 1930's.  Because of the difficulty of producing instrument which agreed with each other within the limits of visual discrimination, the Institute of Paper Chemistry (Appleton, WI) established a "Brightness Standardization System" whereby all newly manufactured brightness testers were matched geometrically, photometrically and spectrally to a master instrument. 

The basis for the 100% brightness point was magnesium oxide. This was chosen since it was the 'whitest' substance available at the time. Since magnesium oxide was very unstable and yellows over a relatively short period of time, more stable opal glass and paper standards were used to transfer this calibration from magnesium oxide to the instruments.  Therefore, calibrated opal glass and paper standards were issued on a monthly subscription basis to allow brightness tester users to maintain close agreement with the IPC master.

TAPPI Test Method T452, which was based on the GE Reflection Meter, was adopted by TAPPI in 1948.  Subsequently, brightness testers conforming to TAPPI T452 have been manufactured by Martin Sweets Company, Diano Corporation and Technidyne Corporation.