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Standard: |
TAPPI |
Method: |
TAPPI T 560 |
Title: |
CIE whiteness and tint of paper and paperboard
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The TAPPI T 560 Whiteness test is used to determine the CIE whiteness and tint indices of white or near white specimens with or without optical brighteners. Whiteness differs fundamentally from paper brightness in that whiteness includes the entire visible spectrum in its assessment whereas brightness includes only the blue portion of the spectrum.
The tristimulus values of the specimen are determined under the conditions specified in this method and the CIE whiteness and tint values are then calculated. The ultraviolet (UV) content of different light sources affects the excitation of fluorescent brighteners to a greater or lesser degree and therefore it is necessary to provide a means of adjustment of the ultraviolet energy.
Paper is bought, sold and used primarily indoors. Therefore it is important to assess the “whiteness” of the paper under similar conditions. When “white” papers are ranked subjectively, it has been shown that people prefer bluish whites to grayish, yellowish, greenish, or pinkish whites. As a consequence, papermakers often add fluorescent whitening agents or optical brightening agents to enhance the appearance of their papers. The CIE whiteness and tint equations have a blue bias to better quantify what people prefer. It has been shown that CIE whiteness values correlate well with visual whiteness assessment when the UV level of the source approximates that of average indoor lighting.
A positive tint value indicates a greenish sample; a negative value indicates a reddish sample. The further the tint value is from zero, the more colored the sample. The perfectly reflecting diffuser has a whiteness value of 100 and a tint value of 0. Whiteness and tint values are not appropriate for strongly colored samples.
Please note:
SGS-IPS cannot sell or otherwise provide standards, specifications, or test procedures to third parties.