Personally i always assumed that lead weighted silk string would be dangerous to health, thus i did not pursue it.
It should be said that silk producers habitually weight silk with all sorts of substances: usually a dyer would be sent raw silk with a simple instructions like: here is 100 pounds of raw silk, i want to have back 150 pounds of black #23. Make it compact, too. As simple as that. The percentage of weighting would be determined by the following: first the silk would be degummed, and loose about 25 pounds out of 100. Then a weighting substance would be added to make 150 pounds, therefore loading would be 100%. As Mimmo correctly stated, 300% can be loaded. What i think is incorrect in Mimmo's assumptions, is that the body of the silk fiber increases so much, as to make it impractical. My doubt is based on the fact that when i inquired with a Shanghai dealer whether they could sell metal weighted silk, he assured me that they 1) can weight with any metal i request and 2) the shipping charges would be lower, as while weighing more, the loaded bails take "mutch less space". To see why, here are some microscope pictures of weighted silk fibers: http://ion.asu.edu/cool61_wtdsilk/cool61_thumb.htm I understand Mimmo's (and other gut string maker's) dismissal of other string materials (and, please understand, i have no investment in silk strings here, i am not selling them, not to imply that profession of string making would make people closed-minded), however "The stringes are made of sheepes and catts gutte" from Burwell next to the "caterpillar XV. The earliest recorded form, catyrpel, is prob. — AN. var. of OF. chatepelose ‘hairy cat’; assoc. in XVI with †piller ravager, plunderer (see PILLAGE), prob. brought about the extended form in -piller, -pillar" next to "catlins" and catgut (see FoRMHI 103, 106, 107, 110), might point towards an area to research. The easiest and clearest argument in this string situation is, of course, the product. Mimmo, in his loaded gut, produced a close to perfect product, that satisfies much of the historic evidence. Until there is a better string, this is where it stands. But, back to the lead's danger to health. I was very much surprised to find this: "The Problem of the Possible Health Hazard of Lead-Weighted Silk Fabric-The increasing use of silk fabrics weighted with lead has suggested this problem to the authors, the purpose of this study being to determine the possibility of lead poisoning from silk weighted with lead salts. The actual experiments took the form of determining under what conditions body fluids would affect the lead salts in silk fabrics and whether absorption of lead occurs in individuals wearing such material. The experiments were carried out by placing 6" squares of the silk in flasks containing measured amounts of liquid. The flask was then rotated in an electrically heated water bath for periods of over 3 hours duration at body temperature. On removal from the bath, measured portions of the suspension were used for analysis. In neutral solutions it was found that the amount of suspended lead was extremely small and that the amount of dissolved lead was either zero or the barest trace, so that microchemical methods yielded very minute amounts. Urine, saliva, perspiration, physiological saline, tap water, and distilled water were tested at normal physiological pH's. Only in the case of saliva, tap water and distilled water micro-chemical methods yielded a positive test. Studies of urine and feces of subjects wearing lead weighted silk garments indicated that no absorption of lead occurs even under extreme conditions, as a result of direct contact of such garments with the skin.-L. T. Fairhall and J. W. Heim, J. Indust. Hyg., XIV, 9:317-327 (Nov.), 1932. L. G." On top of such... may i say nonexistent?.. toxicity, a silk string that is desired to be as smooth as to duplicate the iconographic evidence, would have to be finished with linseed oil and then polished, further reducing any possible leaching. To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
