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[BKARTS] Drape and Throw-up



Tom Conroy has a good examination of drape and throw-up in The Book and Paper Group Annual, #6:

http://aic.stanford.edu/sg/bpg/annual/v06/bp06-01.html



A short excerpt:

Drape and the amount of throw-up needed



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Fig. 1. Good and poor drape. Folio and duodecimo from the same paper; the 12mo is cross-grained as well as narrower.

As the book is opened and closed the cross-section arc of the spine will normally throw up, going from convex to flat or to concave. The degree of throw-up needed will vary with the drape of the text block, modified by the book's thickness and the width of the gutter margin.

Drape is the flexibility of the page over its width. It is not a direct quality of the paper; rather, it is the stiffness of the paper divided by the page width and modified by the format.

A wide page will drape better than a narrow page of the same paper (Fig. 1); for instance the paper used by William Morris drapes well in the Kelmscott Chaucer, but when his imitators used it in duodecimos it draped very poorly. Again, most papers drape better with the grain vertical (folio and octavo) than horizontal (quarto, duodecimo, sextodecimo)1.

The book should preferably open from the bending of the page over most of its width; there should be as little throw-up as is compatible with free opening. I f a book throws up high the stresses and wear of opening are localised at the gutter instead of being spread out across the page. The paper will bend too much at the gutter and will be fatigued; worse, the tension of the sewing thread and supports will change as the book opens and closes, sawing the thread against the stations. A low throw-up is most important when the paper is both very weak and very flexible, as can happen with thin but degraded papers.



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Fig. 2. "Settling down" of a flexibly-lined, tight-back book. The spine may remain slightly convex, especially at the joints, yet still have flattened out enough to be stable when lying open on the table.

Few books have such good drape that a completely rigid spine can be used; most will need some throw-up or the book will not lie flat on the table to any given page. In general the spine should at least flatten out a bit when the book is opened, settling down on the table like a hen on her nest (Fig. 2). If the spine is rigid, especially if the round is high, the book is apt to tip over on the fulcrum of the spine, rocking to the side of the opening with more pages; the pages will flip over as the book tips, and the book will close itself (Fig. 8).



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Fig. 3. Opening of a book with poor drape but high throw-up.

A higher throw-up is needed when the drape is poor (Fig. 3), when the book is thick, or when the gutter margin is narrow (Fig. 4). Thickness and narrow margins have similar effects, burying the text in the gutter where the page is near perpendicular to the table. With poor drape, of course, the pages simply will not settle down.





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