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BRIGHTNESS is the
measurement of how much white light a paper reflects, expressed as a
percentage. No paper reflects 100 percent of the light striking it, but
some come close. Premium coated and uncoated white papers and some
laser papers are rated as high as 97 percent. Paper for business forms
falls somewhere in the 80s--about as low as the lowest rating for any
printed product would be. (At the opposite end of the brightness scale
are items like brown paper bags, which have a brightness rating of
around 20.)
Brightness affects readability: too little means low
contrast and a dull appearance; too much produces glare and eyestrain.
Generally speaking, papers for products like books and technical
manuals are less bright than papers for magazines and advertising
brochures.
OPACITY determines how
visible images from the underside of the sheet will be on the side
being looked at. A paper should have enough opacity to prevent unwanted
images from showing through. Like brightness, opacity is expressed as a
percentage, and most printing papers fall within the 80 to 98 percent
range (although swatchbooks and price books usually don't present these
ratings--select with care).
Mills sometimes add fillers and chemicals to certain
papers to increase their opacity. These papers then are marketed as
"opaque" grades. Another way to get better opacity is to specify a
paper with a higher basis. However, heavier paper costs more to buy and
can add to the cost of binding and postage.
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