n.a measure of a material’s strength based on its ability to sustain folding until it breaksBarrow 1943, 153Upon subjection to accelerated aging tests by baking for seventy-two hours at 100 degrees centigrade, it was found that the silked papers had lost 52 per cent of their folding endurance, those laminated but not treated for acid had lost 31 per cent while those laminated with the acid neutralized had lost but 5 per cent and had no increase in acidity.Barrow 1948, 301The folding endurance test was used to determine the embrittlement of the paper fibers that might result from the ink.Lewis 1949, 13The rate of loss in folding endurance—the only strength property to change in the fifteen years—is approximately the same for each of the papers but, since the purified wood pulp paper had a considerably lower original folding strength, we might expect it to lose its fold sometime sooner than would the paper from the high-grade rag stock.Turner 1957, 330The folding endurance of the films (as measured in MIT Double Folds) ranged all the way from 15 to 293. ¶ Toughness in film can be defined as the opposite of brittleness; it means strength and firmness with flexibility. Folding endurance tests were made in the laboratories of the Bureau of Standards on a plasticized and an unplasticized film cast from the same cellulose acetate flake and on a commercial film suitable for lamination.Lewis 1959, 320It should be stressed that the test employed for determining folding endurance is primarily designed for papers of fairly high strength. Just what its significance is on papers of low folding endurance is questionable. As an illustration of this, we checked the folding endurance of the three types of paper on the MIT folding tester at three tensions . . .Poole 1976, 158Further, we have aged a variety of papers, both those which have been deacidified and buffered and those without treatment, for similar periods of time. In the case of newsprint, folding endurance of the encapsulation was inexcess of 6500 folds.Roberts and Etherington 1982The number of folds which a specimen (usually paper) will withstand before failure, under controlled conditions in a specified instrument. In the usual test, a specimen is subjected repeatedly to double folds through a wide angle while under tension. Folding endurance is a very important indication of the durability of archival papers. A decline in folding endurance is the most sensitive indicator of aging and deterioration of paper.ISO 5626, 19933.2 ¶ folding endurance ¶ Logarithm (to the base 10) of the number of double folds required to cause rupture of the test piece when tested under applied standard stress conditions.
With the onset of defined international preservation standards, folding endurance has been measured by the number of double folds [ISO 5626: Paper – Determination of folding endurance; TAPPI Test Method T 511: Folding endurance of paper (MIT tester); and TAPPI Test Method T 423: Folding endurance of paper (Schopper type tester)]. Before these standards, some nonstandardized techniques measured single folds.