Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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page flex test

A binding endurance test designed to determine the number of times a leaf of a bound book can be flexed under light tension before it becomes detached from the book. The book is placed open on a flat plate, with both covers flat on the surface. A single leaf is selected and held in a vertical position, while the remaining leaves on either side are clamped down. The vertical leaf is passed between two bars approximately 3/16 inch in diameter, 1/4 inch apart, and longer than the leaf, and positioned at a fixed distance of 2 inches above the gutter of the book. A clamp is attached to the leaf to hold it in a vertical position, as well as to exert an upward force of 3 to 5 pounds. The bars on either side of the leaf are moved back and forth a distance of 3 1/2 inches, causing the leaf to flex at an angle of 45° to either side of the vertical, or a total of 90°. The flexing is at the rate of 88 per minute, and the test continues until failure of the leaf, or a maximum of 1,000 flexes. To accelerate the test, the upward force exerted on the leaf can be increased.

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