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Paper Chase - Permajet -The Wholerange - part 3 of 1 2 3 4 5 6 7 8 9 10 11 12 13

by Mike McNamee Published 01/04/2010

The Main Parameters

Base Colour
The 'white' base colour tells us a lot about the paper's properties. White is a complex colour and there are many types of white. A spectrographically neutral white can looka little cream to most eyes and, traditionally, paper makers have added agents to make the paper a little more blue and a little brighter. Colormetrically a cooled paper showsa negative b value in the Lab scale, typically between -3 and -12 Lab points. In addition, optical brightening agents (OBAs) may be added which both cool and brighten a paperby enhancing the reflectivity with a fluorescing agent, an OBA.

Again these take many forms - cooling agents and OBAs are not always one and the same thing. It is possibleto cool a paper white without increasing its brightness by fluorescence. Normally we examine these properties by use of both an ultraviolet viewing booth and a full-rangespectrophotometer. In visual terms a cool, brightened paper is usually described as having more 'pop'. This is a vague term which encompasses the apparent (or real) increasein brightness which lifts the highlights and creates more contrast.

In the graph (right) the papers below the datum line are not brightened, those above have varying degrees of brightening. Thus papers with negative values will bewarmer to the eye while those to the right are arranged in progressively stronger cooling (blueness). Many fine art printers are wary of OBAs as they have been shown toyellow with age (or at least become less blue).

Dmax
This is the density of a deep black (usually 0, 0, 0 RGB values) and represents the deepest black that the paper and printer combination is capable of achieving. Its value dependsupon absorbency of the paper, as ink that is diffused into the base layer of the paper is hidden from view. Very glossy surfaces hold ink near the surface and show as more densewhen measured. Dmax is affected by ink type and its interaction with the media. Matt Black ink is better on matt and art surfaces, but does not take on gloss surfaces.

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1st Published 01/04/2010
last update 09/12/2022 14:59:48

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