Printing knowledge: Paper Characteristics 

Basic Size and Basis Weight

The basis weight refers to the weight in pounds of 500 sheets of paper when it has been cut to that paper's standard basic size. For example the basic size for Bond paper is 17 x 22 inches. If 500 sheets (a ream) of Bond is cut to its basic size of 17 x 22 inches and weighs 20 pounds, it is classified as 20 lb. bond. If a 17 x 22" ream of Bond paper weighed 24 pounds it would be called 24 lb. Bond, and so on. The chart below contains some common paper types and their basic size.

Paper Type	Basic Size
Bond Ledger Offset Book Cover Index Bristol Vellum Bristol Printing Bristol Tag	17" x 22" 17" x 22" 25" x 38" 25" x 38" 20" x 26" 25-1/2" x 30-1/2" 22-1/2" x 28-1/2" 22-1/2" x 28-1/2" 24" x 36"

ISO Size Standards

The International Organization for Standardization (ISO) has established standards for paper sizes based on the metric system (millimeters). The standards have been grouped into three different series of requirements: "A-series", for general printing, "B-series", for posters, and "C-series", for envelopes, postcards, and folders. The "A" series is the most commonly used with sizes ranging from A0, which is the largest, down to A8. The A-series sizes are all represented as a part of the area of one square meter with a length to width ratio of 1.414. The size A0 is equivalent to the area of a square meter with each smaller size being 50% of the size of the preceding one. A1 is 50% of the area of A0, A2 is 50% of A1, and so on. Another way to look at it is that when an A0 sheet is cut in half, two A1 sheets are produced, and when an A1 sheet is cut in half, two A2 sheets are produced. Some of the sizes for the A-series are shown in the illustration below.yellowprinting.com

North American Size Standards

Although the ISO size standards are common in many parts of the world where the metric system is the established standard for measurement, North American sheet sizes are based on inches and are shown in the illustration below.

Universal Web Sizes

The paper rolls shown below are the standard widths used on web presses. The illustration also shows the standard ISO sheet sizes and the standard North American sheet sizes that can be obtained from each roll width .

Caliper Readings

The chart below shows the actual thickness of various weights and grades of paper. The readings are taken with a caliper or micrometer gauge, which measures the thickness of the paper in thousandths of an inch.

Paper Type	Thickness	Paper Type	Thickness
15 lb. Bond 20 lb. Bond 24 lb. Bond	0.003 0.004 0.0045	100 lb. Tag 125 lb. Tag 150 lb. Tag	0.0075 0.009 0.0107
28 lb. Ledger 32 lb. Ledger 36 lb. Ledger	0.005 0.00525 0.00575	4 Ply Railroad Board 6 Ply Railroad Board 8 Ply Railroad Board	0.018 0.024 0.03
50 lb. Regular Offset 60 lb. Regular Offset 70 lb. Regular Offset 50 lb. Smooth Offset 60 lb. Smooth Offset 70 lb. Smooth Offset	0.004 0.0045 0.005 0.0025 0.003 0.004	50 lb. Gloss Coated Book 60 lb. Gloss Coated Book 70 lb. Gloss Coated Book 80 lb. Gloss Coated Book 100 lb. Gloss Coated Book 120 lb. Gloss Coated Book	0.0025 0.003 0.0035 0.004 0.005 0.006
90 lb. Index 110 lb. Index	0.007 0.0085	50 lb. Coated Cover 60 lb. Coated Cover 100 lb. Coated Cover	0.00475 0.006 0.0095

Finish

The finish refers to the surface characteristics of the paper such as how the paper feels...is it smooth such as glossy cover or rough with an antique finish? Does the paper have a glossy appearance such as coated glossy papers or is it dull like bond paper. Does the paper enhance the look of the printed piece similar to watermarked paper or is it purely functional like newsprint? Does the paper have a high ink absorption rate as does Vellum or poor absorption such as on coated papers?Finishes can be applied to paper during the manufacturing process or produced offline. A finish such as Laid can be created while it is being manufactured with the use of a marking roller that forms the pattern in the paper while it is still wet. Paper finishes provided offline are usually accomplished with steel rollers that press the pattern into the paper. The offline finishes are known as embossed finishes. Some common paper finishes are described below.

·         Cockle - A cockle finish simulates characteristics of hand made paper with a wavy, rippled, puckered finish. The effect is obtained by air drying the paper under minimum tension.

·         Felt - Felt is a soft texture on uncoated paper that is created during the paper-making process with a either felt covered roller or with a rubber roller with a felt pattern that creates the finish. It can also be accomplished as an offline process. The felt finish does not affect the strength of the paper.

·         Gloss - A gloss finish produces a shiny and reflective surface on one or both sides of certain coated papers. A higher gloss is usually seen on higher quality coated papers. The gloss finish is produced from compounds added during the paper making process.

·         Laid - A laid finish has the appearance of translucent lines running horizontally and vertically in the paper. It is produced during the paper-making process with a special roller that creates the pattern in the wet paper.

·         Linen - Linen finished paper resembles linen cloth and is usually produced after the paper-making process as an offline embossing process.

·         Matte - A finish on certain coated papers that is smooth but gives a dull appearance. A matte finish, as well as other types of coated paper, are good choices for print jobs in which high quality is required.

·         Parchment - A paper finish that has an old or antique appearance and is the result of washing sulfuric acid over the paper and then quickly neutralizing the acid wash. This process melts the outer paper fibers which fill the voids in the rest of the paper. Parchment is very durable and grease resistant.

·         Smooth - A smooth finish is the result of the paper passing through sets of rollers during the paper-making process. This process is known as calendaring.

·         Vellum - A vellum finish has an eggshell appearance and is consistent and even but not as much as a smooth finish. Vellum is one of the most popular uncoated finishes and paper with this finish has a high ink absorbency rate.

·         Wove - An even finish in uncoated paper with a slight texture made by a felt roller covered in woven wire.

Grain

The grain of the paper refers to the direction of the fibers in a sheet of paper. Long grain paper refers to paper in which the fibers run in the same direction as the longest measurement of the paper. On rolls of paper for web presses, the grain runs along the length of the web. Short grain paper refers to paper in which the fibers run in the same direction as the shortest measurement of the paper. When paper is torn, it will tear easier and straighter when torn parallel with the grain. It will also fold easier parallel to the grain and produce a cleaner fold than if folded across the grain. Laser printers require long grain paper for the best results. Short grain paper may not feed properly into a laser printer and the heat produced by a laser printer may result in the sheets curling as they come out of the printer. 

Whiteness

The whiteness of paper is the measure or its ability to reflect the colors of light equally. The more evenly a paper reflects all colors of the spectrum, the whiter the sheet. Some papers may reflect slightly cool colors back to our eyes and give the illusion that the sheet is actually brighter than white paper. If white paper has a slight warm appearance it will not appear as bright as a sheet that reflects a cool color, however warm colors printed on a warm sheet will appear stronger than when printed on a cool sheet. Cool colors printed on a cool white sheet are also enhanced in the same way. There is no such thing as a pure white sheet of paper, since the white that we see is always influenced by the lighting of our environment and the reflections from surrounding objects.

Grade

The grade of a paper refers to the type or category of the paper contents which provide a level of brightness or surface characteristics used to determine the grade level of the finished paper stock. Grades are classified from "Premium" at the highest level to "5" at the lowest level. Some text and cover stocks are listed simply as A or B grades since fewer grades of the text and cover stock are produced. A table illustrates the grade levels of paper according to the degree of brightness.

Brightness

Brightness refers to the percent of light reflected back from a sheet of paper as measured by a light meter reading. Contrast is reduced and highlights are not as strong when paper with a lower brightness is used for a printed piece. The quality and brightness of paper is organized into six categories:

Paper Brightness
Premium Number 1 Number 2 Number 3 Number 4 Number 5	Quality Quality Quality Quality Quality Quality	= = = = = =	88.0 to 95.0 Brightness 85.0 to 87.9 Brightness 83.0 to 84.9 Brightness 79.0 to 82.9 Brightness 73.0 to 78.9 Brightness 72.9 and below

Opacity

Opacity is the measure (percent) of the amount of light passing through a sheet of paper. Some papers have more fibers and/or fillers and as a result are more opaque than others. Papers containing more fibers and fillers have the ability to hold a printed image without showing through to the backside as easily as papers without as many fibers and fillers. Just because a paper is thicker does not guarantee that it is more opaque than a thinner paper. Some thinner papers may be more opaque because there are a greater number of fibers and/or fillers in their composition. 

Smoothness

The smoothness level is a measure of the surface characteristics of paper. The flatter or more even the surface, the higher the level of smoothness. With a smoother surface, the stock can provide a fully shaped ink dot resulting in a sharper and higher quality image.

Holdout

Holdout refers to the property of ink remaining on the surface of the paper rather than soaking in. A coated glossy paper has a high holdout rate while a paper stock such as newsprint or 20 lb. Bond has a high absorption rate or a low holdout rate. 

Acidity/Alkalinity

The pH (potential for Hydrogen) measurement of paper determines the degree of acidity and alkalinity in the stock. The pH scale has readings of 0 to 14 with 7 being neutral. Readings below a pH of 7.0 are acidic and above are alkaline. Each single digit actually equals a measure of 10, so a stock measuring 4.0 pH is 20 times more acidic than one measuring 6.0 pH. Paper can have an acid base, an alkaline base or it can be neutral with a pH of 7. Most paper manufactured in the 20th century was of an acid base. Acidic papers deteriorate in a relatively short period of time, and should never be used for printed items that are intended to last for many years. Since the 1970's, most of the paper used for book publishing and other printed materials where permanence is of importance, has been alkaline paper, which lasts much longer than acid based paper. Alkaline paper is manufactured with fillers such as calcium carbonate, which bring the pH above 7. An acidic paper like newsprint has a pH around 4.5 which becomes lower once it is printed. The acid level tends to break down the paper and it can deteriorate rapidly, which is why newspapers tend to yellow and fall apart in time. Alkaline paper (a pH above 7) is said to be permanent, but papers that have a neutral pH are still best for preserving items like photographic albums and as matte boards for artwork.

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