1. A 3D printer with filament authentication, comprising: a print engine for generating a 3D object using a filament of material; and an infrared (IR) authenticator positioned to authenticate the filament before use by the print engine the IR authenticator comprising: an IR generator for generating IR at a first wavelength; and an IR detector for detecting fluorescence of a dye within the filament at a second IR wavelength; wherein the authentication of the filament is based upon detection of the fluorescence at the second IR wavelength; wherein operation of the print engine is based upon authentication of the filament by the IR authenticator.