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Chains for Bows
Part 2 of 3

"After the worm has finished its spinning, which takes about three days, the cocoon is placed in steam to kill the worm and then in hot water to dissolve or soften the wax so that the girls with twigs may find the outer end of the cocoon thread. It is then reeled. From two to ten cocoon threads are wound together on large reels. When removed from the reels, it is twisted to form what is called a hank. The next process is that of throwing. This consists of reeling several of the threads from hanks together and in some cases giving the whole a twist. The wax is then washed out and after re-reeling, the silk is ready for weaving or knitting. The average size of the double thread from a cocoon is about three denier. A dinier is a thread that weighs .050 grains per 450 meters of length."

Certain moths are allowed to hatch from the cocoons in order to perpetuate their kind. The cocoons broken open by the emerging adult are unfit for reeling, but have other uses.
The cocoons are rushed by the farmers to various cocoon markets where their crops are turned into cash. Speed in transit is essential, for there is always danger of the moths emerging en route.

"Having explained the nature of the long elastic chains that are recommended for backing bows, we may explain how the chains are put into proper form for applying to the bow. The silk throwers use about eight cocoon threads (22 denier), they throw 23 of these together in untwisted form with the wax removed. About 25% of the silk as purchased in the raw state is gum. The silk thus prepared for me is put up on tubes marked 22-23 ends. This means twenty three strands of silk weighing 22 denier. The silk in this form is passed through a bath of glue and wound on to drums that are 72 inches in circumference. Two layers of 100 threads per linear inch are wound on the drum. After drying, the sheet is split and removed from the drum. We now have about 37,000 cocoon threads per square inch with of sheet. The tensile strength of the sheet is about 38,000 pounds per square inch. The strands are wound on the drum with as much tension as the glue will held. If removed before the glue sets, the sheets would be only about 71 inches long. Thus, we not only have the long chain molecular structure, but the chains are all stretched ready to take hold the moment the bow is bent. Due to the high elastic limit of silk, it may be further pretensioned at the time it is applied to the bow. In addition to the tension In the silk In sheet form, an additional 3% stretch is available, leaving 1% for the stretch due to the bending of the bow, the silk may be stretched 2% at the time it is applied to the bow or stave. That means that a 72" strip may be stretched as much as inches. It should be clearly understood that the sheet, If properly clamped, may be stretched 10% before it will break. However, during the last 7% stretching it does not have perfect elasticity. It will not completely return to its original length. In this respect it is like the wood of the bow. The wood takes a permanent set long before it breaks. Steel has almost perfect elasticity up to the breaking point. Nylon, as mentioned before, has almost perfect elasticity up to the breaking point which is 13% elongation. Nylon would make a good backing for bows if a suitable binder is found for it. I have done considerable experimenting with it, but so far have not found any binder that will hold the high stresses required. It could not be used without prestretching because its modulus of elasticity is too low, being about one third that of silk. The silk has a tensile strength of from five to seven fold that of bow woods so that the use of Nylon might not help much unless, we find a material more suitable for the belly of the bow. A bow with a horn belly might be improved by using Nylon backing instead of silk. A pretension of 2% stretch of the silk is too much for some yew woods and green lemonwood. Osage will stand the limit."