I'm pretty sure it is acrylic these days and the word celluloid is used to give an old school sound.The 'real' celluloid is fragile,does degrade in colour(even shape)and can spoil other knives near it.But, I don't know how long this process takes,years or decades?
Faux tortoise is used but does anybody know if real tortoise-shell was ever used on knives? It certainly was on spectacle frames and knick-knacks in the last century and before. I have a whole tortoise shell (the occupant must have vanished decades ago..)as an ornament in the hall.Wonder how durable this kind of 'bone' is, it has ready made jigging already!