Finishing three-dimensional printed parts

A system comprising:

• a three-dimensional (3D) printer;
• a post-processing component;
• a processor;
• a memory coupled to the processor and store instructions executable by the processor to:
• determine a finishing operation to be performed by the post-processing component on a portion of a part after the part has been 3D printed by the 3D printer;
• cause the part to be 3D printed by the 3D printer to include a marking on or in the portion that indicates the finishing operation that has been determined such that the marking has a fluorescent color having a brighter color under ultraviolet or near-infrared light than the portion or such that the marking has a magnetism different than a magnetism of the portion;
• and
• a sensor to optically or magnetically detect the marking on or in the portion of the part after the part has been 3D printed,
• wherein the instructions are executable by the processor to further, after the part has been 3D printed, and in response to the sensor detecting the marking:
• determine the finishing operation indicated by the marking;
• cause performance of the finishing operation by the post-processing component on at least the portion until the sensor no longer detects the marking on the portion,
• and wherein the finishing operation includes:
• ejection of a substance to remove material from at least the portion of the 3D printed part or to add material to at least the portion of the part;
• subjecting the part to a chemical bath deposition to add material to at least the portion of the part;
• or
• removal of material from at least the portion of the part.