In an example, a method includes operating, by a processor, on object model data. The object model data describes at least part of an object to be generated in additive manufacturing. The method also includes determining, by a processor, pattern data. The pattern data comprising areas of variable reflectance intended to be formed on a portion of the object. The method includes determining, by a processor, object generation instructions to apply a fusing agent to at least part of a layer of build material corresponding to the portion of the object in a density corresponding to the reflectance of the generated pattern data.