Chapter XVI: Appendix: A

SPECIFICATIONS OF THE U. S. BUREAU OF STANDARDS FOR BOOK CLOTHS

FABRIC

The fabric shall be made from first-quality staple cotton, uniformly woven and of a grade known as "firsts." The weave shall be two up and two down in the warp and one up and one down in the weft.

The gray cloth shall consist of from 33 to 36 threads per centimeter (85 to 90 per inch) in the warp, and 12 to 15 threads per centimeter (30 to 38 per inch) in the weft.

The surface shall be finished smooth and hard and show no tendency to stick when folded upon itself.

THICKNESS, TENSILE STRENGTH AND WEIGHT

The thickness of the finished fabric shall not exceed 0.30 millimeter (0.012 inch) or be less than 0.20 millimeter (0.008 inch). The tensile strength of the gray cloth shall be not less than 18 kilograms per centimeter (100 pounds per inch) of width in the warp, and 9 kilograms per centimeter (50 pounds per inch) in the weft. The average value for the warp and weft in the finished fabric must show an increase over the average value for the warp and weft in the gray cloth of at least 10 per cent of the strength of the gray cloth.

The finished fabric, when dry, shall weigh not more than 250 grams per square meter (0.5 pound per yard), or less than 200 grams per square meter (0.4 pound per yard).

ABSORPTION OF MOISTURE

At a normal relative humidity of 65 per cent it shall not absorb more than 5 per cent of moisture, or expand (an average of both directions) to exceed 0.45 per cent, and when subjected in a closed case to a saturated atmosphere for two hours at a temperature of 20 deg. C. (68 deg. F.) shall not absorb more than 10 per cent of moisture or expand (an average of both directions) to exceed 2 per cent. All increases to be computed on the basis of the dry weight and dimensions.

FOLDING ENDURANCE

The folding endurance, as determined by the Schopper folder, shall be not less than 65,000 double folds for the warp and not less than 10,000 for the weft.

COLOR

Before coating, the fabric must be dyed with a purely mineral or inorganic color (such as iron salts), so as to imitate the color of the finished cloth, but somewhat lighter in shade, so as to give the desired "linen" effect. All coal-tar, aniline, vegetable, or other organic dyes and lakes must be strictly excluded from both fabric and coating, even in traces; except where necessary to match color, lake may be used in red, blue, or brown. The following substances must be also excluded: Chrome yellow and other chromates, ultramarine, browns containing bituminous or other organic matter, compounds of lead and arsenic.

The color of the finished fabric should be slightly darker than the standard sample, which will be furnished on application, and it must not show the slightest change of color after exposure under prescribed conditions to direct sunlight, or to the action of ammonia gas, sulphuretted-hydrogen gas, sulphur-dioxide gas, or illuminating gas.

RESISTANCE TO MOLD AND INSECTS

The finished fabric shall be immune to the growth of mold or the attack of insects.

TESTS

Physical and chemical tests to verify the properties required by these specifications will be made according to the "Standard method for testing book cloths" as used by the Bureau of Standards, copies of which can be obtained on application.