Much like zeroing in on the right shade of white paint for your walls, the right shade of white paper can have a serious impact on the final appearance of your print job.
When specifying paper for a print job, there are some basic properties that are generally used to direct that decision.
- Brightness is the most familiar measurement used to express the lightness of white paper. It is an indicator of what the human eye perceives as light versus dark shades of white. Brightness focuses on a very narrow band of reflected light in the blue region of the visible light spectrum. It does not tell the consumer anything about a paper’s shade, which may have a significant impact on perceived brightness/whiteness.
- Whiteness is a measurement that goes beyond brightness by looking at the shade of white paper. Most people perceive bluer shades to be brighter and Whiteness, like Brightness, puts a heavy weighting on blue shades. For this reason, Whiteness measurement can yield high values for papers that may look more blue than white.
Shade or Color
L,a,b (L,a,b) values are the way color or shade is measured. L,a,b values will be specific to the instrument on which they are measured. The “L” value is a measure of “lightness” along a black/white axis. The “a” value is a measure of red/green. The “b” value is a measurement of blue/yellow.
To ensure consistent color production, corporate shade standards are maintained in freezers. Yes, that’s correct. Keeping the samples in the freezer helps maintain their integrity.
Each mill that makes a specific shade of white paper has physical samples taken from the same manufacture lot that are used for color matching. Tolerances and allowable variation are based on the measured values of the freezer samples.
Testing for Functionality
The paper machines have in-line equipment that constantly measures brightness and shade during production. Closed-loop systems automatically adjust dye flows and other chemical additives to maintain brightness and shade within tolerances. The tolerances were developed to ensure a commercial match between production runs and to prevent mixed shades of white paper from ruining an otherwise awesome print job.
In the lab, we measure Brightness, Whiteness and shade using various benchtop testing devices. Some papers are blue-white, others are redder or greener and then there is the whole family of “cream” whites. So, how do we consistently produce paper that is the same shade of white? We TEST it.
To measure Brightness we use a TAPPI brightness meter. This is a paper industry standard and has a single, specific light source and measurement angle.
Brightness was originally developed as a manufacturing tool and thus is limited in its usefulness. It focuses on a very narrow band of reflected light in the blue region of the visible light spectrum. Higher numbers indicate “brighter” paper. It does not tell the consumer anything about a paper’s shade.
To measure color or shade, we use a spectrophotometer. A spectrophotometer records reflectance at multiple wavelengths within the visible light spectrum and includes light reflected from all angels. A spectrophotometer can provide a more thorough analysis of shade, but not a true measure of TAPPI brightness. The values generated by the spectrophotometer will provide the L, a, and b coordinates of the paper’s color.
The spectrophotometer also measures Whiteness. Whiteness is a measurement that goes beyond brightness by looking at the shade of white paper, considering reflected light in the red, yellow, and green as well as the blue region of the spectrum.
Although higher values indicate a “whiter” shade of papers, the measurement can yield high values for papers that appear more blue than white. The end goal of all of this testing is to make certain that the paper not only meets its advertised brightness but that the shade of white is consistent every time.
Selecting the Right Shade of White Paper
The choice is yours to make. As you select the Brightness and shade of white for your job keep in mind that offset printing inks, for the most part, are transparent. The color of your paper can significantly impact the color of your printed output.