Amber Strings by #Warchal. Available for Violin and Cello at @infiniti_strings. . . The Amber string set has been developed with the aim of achieving the sound quality of the best gut strings without any tuning instabilities. The set features W-Core®, a completely new core material developed by Warchal's Research & Development team. The sound is rich and warm, but still has texture. . . The Amber E string is based on Warchal's newest unique invention. This solution increases the longitudinal elasticity of the string, which results in a significant sound improvement and no whistling.