The sulfurization consists in putting the loom on which the twisted and still damp gut strings have been stretched inside a hermetically sealed environment in which sulfur is burned to obtain sulfur dioxide.

It is an ancient technique created to whiten the gut once twisted, which otherwise, once dry, would appear brown.

In reality the sulfurization not only serves to make the strings transparent and of a beautiful golden color, but also to obtain a greater elasticity and sonority of the same: after the treatment the strings appear in fact of almost rubbery consistency, before drying out, perhaps later to a chemical process of vulcanization, as Mimmo Peruffo hypothesizes.

This additional effect, already noted by ancient sources, obviously cannot be achieved by bleaching the strings with hydrogen peroxide, now used by all modern string makers for practicality.