3 GENERAL INTRODUCTION TO PAPER TEXTURE

The science of describing and measuring surface texture is in its infancy, although aesthetic appreciation of paper surface texture has been with us as long as paper has existed. At one time paper was merely an economic replacement for the celebrated and romanticized vellum leaf. Over time, the romance and appreciation of paper have generated great appreciation for paper texture in all its forms: smooth, glossy, rough, original, calendared, hot pressed, coated, pebbled, and so forth. Specialists can distinguish even an expertly treated sheet from a never washed sheet by subtle differences in texture and drape.

The scientific vocabulary for texture is not established. In our work, we have found that the generic term “surface texture” is actually composed of three discrete domains. The smallest textural domain concerns the fibers as they are adjacent to one another, generally within one square mm; this is called “surface grain.” In the range of one square cm, clumps of hundreds of fibers are offset from one another in the third dimension; this is called the “surface texture.” On the largest scale, a 10 cm (4 in) square, whole regions of a sheet can be higher or lower than the adjacent region; this is called “cockling.” All these features can be seen with the eye; all can be photographed using raking light. Surface grain can be perceived by the eye and can be seen in some fine-grained, well-shot raking light photographs, but it is most effectively visualized at 22x using raking light.1 Surface texture is perceptible in raking light and easy to see at 2–5x using raking light. Cockling is clearly discernible in raking light.

Quantifying changes in surface texture is difficult. After extensive practical research into the analytical quantification of paper texture, we found that statistical analysis of the observations of a large group of practiced observers proved to be the most successful methodology.