Tortoise Shell was considered the "Holy Grail" of guitar picks forever!   The search has been modified for years to try  to make picks which are legal and non-lethal to life forms, and which get the same sound.  Casein (a resin made from milk) came about and the folks at John Pearse found that they were perfect for the faux tortoise shell.  Includes a cloth pouch to keep your exquisite guitar pick safe!