Celluloid remains in use for musical instruments, especially accordions and guitars. Celluloid is very robust and easy to mold in difficult forms, and has great acoustic performance as cover for wooden frames since it does not block wood's natural pores. Instruments covered with celluloid can easily be recognized by the material's typical nacre-like flaming pattern. Thick celluloid panels are cooked in a bain-marie which turns them into a leather-like substance. Panels are then turned on a mold and allowed to harden for as long as three months