Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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A high grade of hard, tough binder's board, dark brown to black in color. It has a smooth finish produced by rolling or milling under high pressure. Originally, millboard was produced from old tarred rope, sacking, and similar materials and was called "black board" or "rope board"; however, genuine rope millboard is now virtually impossible to obtain, except from covers discarded from old bindings. It is now made from waste paper, various wood pulps, screenings, with the better grades containing some hemp and flax fibers. The sheet is produced on a wet machine and is calendered by passing it through a board calender several times. The final thickness of the board generally ranges from 0.036 to 0.144 inch.

Old millboard contains sufficient iron impurities to promote the formation of sulfuric acid due to the presence of sulfur dioxide in the atmosphere, much in the same manner as in paper, although at a much slower rate. Millboard, furthermore, often suffers from an additional defect from the point of view of the bookbinder, namely, excessive lamination stemming from the pressure used in calendering. This excessive lamination can cause the corners of the boards to be subject to splitting and mashing.

Rope fiber millboards were first produced in the late 17th century, but they were not in general use until perhaps the first and possibly the second decade of the 18th century, and even then only in the superior grades of binding. The cheaper machine-made boards were in use as early as the 19th century. Millboard was used continuously until the Second World War in the better grades of binding. (82 , 161 , 198 , 236 , 335 )

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