V. Write a short summary of the text

Text 5 Specifying papers

When purchasing paper great care must be exercised in specifying the quality and quantity required. The following are a few of the most important considerations.

Substance This refers to the weight of the paper and in the UK and most of Europe, the metric system is used where paper substance is described in grammes per square metre (gsm) — the weight in grammes of a sheet of the paper having an area of one square metre. In the USA and certain parts of the Far East, substance is described as the weight of a ream (500 sheets) of paper in a certain standard size. For example, a book paper might be described in the USA as having a substance of 60 pounds. This means that a ream (500 sheets) of the basic size of 25 x 38 inches weighs 60 pounds. The conversion table on page 154 enables substances of both systems to be compared. Size In the metric system, sheet sizes are given in millimetres, as are reel widths. In the USA, sizes are given in inches. For large jobs, such as long runs of books or magazines, the paper may be made specially for each job and (depending on the width of the paper making machine) can be made to virtually any size. Smaller jobs have to be printed using standard sheet sizes and in the metric system, these are the 'A' and 'B¹ series of sizes. Most books are produced in sizes related to the system in use before metrication, so have sizes in millimetres for trimmed page size and sheet size.

Grain direction (for sheet-fed paper) is the direction in which the web of paper runs through the paper making machine with the result that the fibres tend to lie in this direction. When specifying paper it is important to state the gram direction for two reasons. In binding, pages open more easily and the book handles better if the gram direction of the paper runs parallel to the spine, also there is less strain in the binding edge. In printing, the printer normally prefers the grain to run across the printing direction as this helps to prevent stretching through pressure or change in moisture content.

Sometimes these two requirements conflict with each other and usually the printing requirement takes precedence. To specify gram, state whether the sheet is long grain (LG) or short gram (SG), depending on whether the longer or shorter dimension of the sheet runs with the gram. When filling out an order form, the machine or grain direction should be the second dimension. Obviously, in web-fed printing, the grain always runs round rather than across the reel.

Bulk This is used to describe the thickness (caliper) of the paper and is mainly used in book production (for example, volume controlled papers). To achieve bulk, it is not always necessary to increase the substance (weight) of a paper. Certain papers such as antique wove can be made bulkier by being manufactured with more 'air¹ in the paper without increasing the weight. It is therefore possible to have paper of a common substance but with several different bulks.

The metric system used in the UK and Europe describes bulk with a volume figure which gives the bulk in millimetres of 200 pages of a lOOgsm paper. Therefore the thickness of the sheet in microns is the weight multiplied by its volume divided by 10, so 80gsm vol 18 gives a sheet with a thickness of 80 x 18- 10 = 144 microns.

In the USA, bulk is expressed as a 'bulk factor¹, which is the number of pages that make a thickness of one inch.

Shade or tint must be specified. Paper manufacturers will offer their standard shades but when a special one is required, it is advisable to submit large samples for colour mate Beware that some papers are 'metamenc' — that is, they e: different shades under different lighting conditions. White fact, the most difficult shade to specify and match.

Exercises :