These are the materials used.
Clear celluloid tubes and black celluloid for the ink deposit and section, and cellulose acetate for the sleeve.
Cellulose acetate will never be in contact with the ink. Celluloid goes inside the sleeve, so the piston runs only on the celluloid, and the ink will only be on the cellulid part.
Celluloid is glued very strongly to the cellulose acetate and will form a one piece barrel.