Paper: It’s a Question of Brightness
If I told you that white catalog paper can have the same brightness measurement as a trendy purple sheet, you’d probably wonder from which planet I hail.
But it’s true. Brightness often is a critical determinant in paper specification, but it’s an attribute whose measurement has fallen prey lately to a wide variation.
That wasn’t always so. When first established, it measured the brightness of pulp by evaluating and controlling the degree of bleaching during the pulp-cooking phase of production. Pulp manufacturers used uniform processes and instrumentation to assess brightness, which resulted in an apples-to-apples comparison and a consistent standard to help classify grades of paper.
However, things are different now; ambiguity has taken center stage in many quarters of the paper industry. Today, a brightness measurement reflects the brightness of the pulp and the paper.
Why does that matter? To influence brightness, most white paper manufacturers use some level of fluorescent whitening agents (FWAs). FWAs increase the “perceived whiteness” of paper. Bear in mind, they’re not inherently bad, but they do pose some problems.
For starters, paper that has achieved its brightness through the use of FWAs can’t be measured in a meaningful way for that brightness, because different brightness instruments currently in use (e.g., Datacolor Elrepho, Technidyne ColorTouch) read FWAs differently. In other words, the same sheet of paper can have different brightness measurements depending on the equipment used to evaluate it. (This is one reason some foreign sheets have higher reported brightness levels than U.S.-made sheets.)
Moreover, controlled conditions and standardization are lacking when it comes to the characteristics of the filters, the light sources (that is, a light’s UV content at the moment of measurement), the direction of the light, the mode of observation, etc.
Ambiguous results present a predicament for every paper specifier selecting product based on the convenience of a brightness measurement. Without knowing the degree of FWAs, the measurement process and the instrumentation used, how can you fairly judge different papers simply by a brightness number? The simple answer is that you can’t.