What are violin strings made of? Well, way back when…
The very first violin strings were made from the natural fibers found in sheep or goat intestines, and here’s how they did it.
As soon as the animals were killed, the intestines were removed, cleaned of all fecal matter, freed of fat, and put into cold running water. The fat had to be removed quickly or the fibers wouldn’t bond properly while they were drying, while the feces had to be washed off or it would stain the strings. The cold water helped preserve the color and strength of the intestinal casing.
Once the submucosa membrane had been softened (for a few hours to several days, depending on the dresser’s preference), the external membranes were scraped off and crushed with a metal-bladed scraper on wooden boards. The goal was to strip off the outside layer and crush the inside membrane of mucosa at the same time. If it was done properly, the inside layer would liquefy and could be squeezed down the casing tube and out. The remaining casing was now a clean tube of muscle.
Casings were sorted into piles according to their thickness, and the lower sections of the casings were preferred for strings—because of their width of 18-20mm, but also because longer fibers were present in the casing of that section of the intestine. Longer fibers made for stronger strings.
The selected casings were still uneven, because different sections of the casing had shorter or longer muscles, so they had to be stretched to make them all even. The string maker used a splitting horn to split the gut string into ribbons that could then be stretched more evenly.
Once even, the strings were twisted on a twisting rack before sitting in in an alkaline solution to break down all oils and fat and leave only the fibers. The solution was monitored and changed frequently, and the gut was scraped at least once a day for four days. Then the gut was whitened by putting the twisting racks of strings in a small, tightly sealed room before setting some sulphur powder on fire in it. This changes the compounds in the air to whiten the strings.
Thin strings only needed 3-4 guts twisted together, like the violin E string, while the D string needs 15. Once the twisted strings had dried — a long process— the strings were polished down with horse hair pads that were treated with oil and pumice powder, to the diameter that was needed.
These days, specialty string makers still make catgut strings, but they usually use a centerless grinder to grind and polish the strings down to the right diameter. The strings are then bleached, disinfected, and sometimes dyed. They are now the most expensive strings one can buy, but many violin players of classical and baroque music will not use anything else because of the unique, rich tone the strings produce.