Paper and ink testing

A variety of tests are used to determine ink and paper and paperboard quality, and to measure their interactions. They are necessary to balance print quality, cost, and wear on the press.

Some of the paper and ink tests are listed here:

I. Paper test A wide variety of paper tests are available, depending on the specific needs and on the governing contract or specification:

II. Ink and Paper (Printability Tests)

III. Ink

The mass per area of the paper is measured as gsm (grams per square meter). Paper sheets are cut to a size of 10 cm x 10 cm, then the sheets are massed individually. The mean of the masses is used to calculate the mass of the paper per square meter, and the standard deviation is determined from all samples. If the mass is higher than specified, it is a loss for the publisher.

Paper shade plays a significant role in the quality of colour reproduction. The shade of the paper affects the colour values of the primary and secondary colours and hence the colour gamut of a press. The standard for paper shade of newsprint as per ISO 12647-3 is mentioned in the table.

The maximum tolerance specified is ∆L 4, ∆a 2 and ∆b 2. When selecting a paper for production, it is very important to measure the paper shade. A spectrophotometer or a spectrodensitometer can be used. Publishers should also check for batch to batch variations. The ultimate aim is to use the paper which has a shade closer to ISO specification.

The colour produced by ink depends on the ink composition, pigments and also the paper shade. This test can be done in two ways. 1. Same ink printed over different paper substrates and 2. Different ink samples printed over a standard newsprint that matches ISO specification.

The most important thing that should be noted is the colour of the inks at the ISO specified density i.e. C 0.9, M 0.9, Y 0.9 and K 1.1. The ∆E value between ISO specified colours and the colours produced by the sample ink gives the ink's deviation from standard.

The colour values of the secondary colours (R, G and B) are also measured. From the colour values of C, M, Y, R, G and B, a 2-D curve of the colour gamut can be plotted and compared with the ISO colour values.

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