Page 190 - Graphic Design and Print Production Fundamentals

178 Chapter 6. Imaging
It is important to keep grain direction in mind when choosing a paper for a project. You need to consider
the print process and binding or finishing method you will use, as choosing the wrong grain direction can
produce poor results or may be incompatible with the printing method you have chosen. Sheet fed offset
lithography papers are often long grain and are most common. Digital presses require the grain to run
perpendicular to the feed direction in order to feed properly and make the sharp turns typically found in
a digital press. In this case, most sheets are fed into the press with the short edge first therefore requiring
short grain paper. When folding is required, folds that run parallel to the grain will be smooth and sharp
while folds that run across the grain will be ragged, and the fibres on the top of the sheet may pull apart.
Toner used in digital printing bonds to the surface of the paper and does not penetrate. Folding across
the grain will cause the toner to break apart where the fibres separate.

The second or underlined dimension of the sheet will indicate the direction of the grain. For example,
18″ x 12″ is a short grain sheet, and 12″ x 18″ is long grain. If the underline method is used, short grain
would be 12″ x 18″ and long grain would be 12″ x 18“. If the dimensions are not noted or the sheet is not
in its original packaging, grain direction can be determined by folding the sheet along both dimensions.
As noted previously, a fold that runs parallel to the grain will be smooth and sharp while a fold that runs
across the grain will be ragged. You can also gently bend the paper in either direction. The bend running
in the direction offering the least resistance is the grain direction.

Caliper

Caliper, unlike grammage and basis weight, is a measure of thickness. The most common measurement
used in North America is thousandths of an inch, designated as points (common for paper) or mils
(common for synthetic paper). This terminology can be confusing, however, as points can also refer
to 1/72 of an inch when referring to font size, line thickness, and dimensions on a page. Mils can be
confused with millimetres as well. A common misconception is that points and mils can be converted
to grammage or basis weight. This is not true. The caliper can vary depending on the coatings or finish.
In general, a rougher finished stock will have a higher caliper than the same weight of a smooth stock.
Coatings can be heavier than paper fibre so coated paper can have a smaller caliper than the same weight
of an uncoated counterpart. A process called calendaring, which irons the paper between two highly
polished chrome rollers, improves smoothness and printability but also reduces the caliper without
changing the weight of the paper.

Brightness and Whiteness

Brightness and whiteness define the optical properties of paper and differ mainly in how they are
measured. Whiteness measures the reflective properties of the paper across the entire visible spectrum
of light (defined by CIE). In other words, it defines how white the paper is. A perfect reflecting, non-
fluorescent white material measures 100 whiteness. Brightness also measures the reflective properties of
paper, on a scale of 1 to 100, but specifically in the blue area of the spectrum at a principal wavelength
of 457 nanometres and 44 nanometres wide (defined by TAPPI and ISO standards). This wavelength
coincides with lignin absorption. Lignin is what binds the cellulose fibres in wood and pulp and gives
it its initial dark brown colour. The more bleaching done to the pulp, the more lignin is removed, and
the higher the blue reflectance and therefore brightness. In most parts of the world, paper whiteness