British cellist Steven Isserlis is according to the BBC’s list of greatest cellists of all time number 13, just below Mischa Maisky and Luigi Boccherini. I must have heard him play at one time, because he is a regular at the Amsterdam Cello Biënnale, a festival that I usually binge. Interestingly, he plays gut strings.
Most cellists play strings made of metal. They are usually different alloys, with a steel core wound with metal. Gut however, refers to the use of animal intestines to make the core of the string. This is done by a specialist string maker, by using fresh intestines from the abattoir, selecting the right specimens, twisting, drying and polishing them. Sometimes the resulting gut is wound with wire, just like the metal strings.
Gut strings have been in use since hundreds, maybe thousands of years. The sound of the gut string forms the reference for the sound of bowed instruments. The highest praise one can give to the sound of a string is that it has the warmth and depth of gut string. What it usually lacks is volume and projection. Modern string are just louder, more in your face.