Classical guitar for repertoire of all periods is sometimes critically viewed: Torres and post-Torres style modern guitars (with their fan-bracing and design) have a thick and strong tone, very suitable for modern-era repertoire. However, they are considered to emphasize the fundamental too heavily (at the expense of overtone partials) for earlier repertoire (Classical/Romantic: Carulli, Sor, Giuliani, Mertz, ...; Baroque: de Visee, ...; etc.). "Andrés Segovia presented the Spanish guitar as a versatile model for all playing styles" to the extent, that still today, "many guitarists have tunnel-vision of the world of the guitar, coming from the modern Segovia tradition". While fan-braced modern
Classical guitar strings the main alternative to nylon strings. The three treble guitar strings are made from sheep or cow intestine, referred to as plain gut, while the three bass strings are made of a silk thread core wound with gut. Since the development of nylon guitar strings by Albert Augustine Ltd., the three treble strings are a single nylon filament, while the three bass strings are made of a core of fine nylon threadlike filaments wound with silver-plated bronze or copper wire. Up until the Second World War animal gut and silk were the materials from which guitar strings were manufactured. Albert