EMBEDDED FEATURES IN THREE DIMENSIONAL PRINTED PARTS

1 . A method, comprising:

dispensing a layer of an optically clear build material;

dispensing a fusing agent onto a first portion of the layer of the optically clear build material;

dispensing an invisible fluorescence compound onto a second portion of the layer of the optically clear build material, wherein the invisible fluorescence compound is to print an embedded feature in the layer of the optically clear build material that is invisible under a first light and visible under a second light; and

applying ultraviolet (UV) light to the layer of the optically clear build material to fuse the first portion and the second portion of the layer of the optically clear build material that received the fusing agent and the invisible fluorescence compound.

2 . The method of claim 1 , wherein the fusing agent comprises a colorless ultraviolet (UV) fusing agent.

3 . The method of claim 1 , wherein the second portion of the layer of the optically clear build material also receives the fusing agent.

4 . The method of claim 1 , wherein the invisible fluorescence compound is formulated with a UV absorber to act as a second fusing agent.

5 . The method of claim 1 , wherein the optically clear build material comprises a thermoplastic polyamide.

6 . The method of claim 1 , further comprising:

repeating dispensing the layer of the optically clear build material, dispensing the fusing agent, dispensing the invisible fluorescence compound, and applying the UV light until printing of a three-dimensional part is completed.

7 . A three-dimensional printed part, comprising:

layers of an optically clear build material; and

an embedded feature printed inside of the optically clear build material, wherein the embedded feature is printed with an invisible fluorescence compound such that the embedded feature is invisible under a first light and visible under a second light.

8 . The three-dimensional printed part of claim 7 , wherein the embedded feature comprises a security mark.

9 . The three-dimensional printed part of claim 7 , wherein the first light is light having a visible wavelength of light, and the second light is an ultraviolet (UV) light.

10 . The three-dimensional printed part of claim 7 , wherein the optically clear build material comprises an optically clear plastic.

11 . The three-dimensional printed part of claim 7 , wherein the invisible fluorescence compound is dispensed as an aqueous jettable formulation.

12 . A three-dimensional printer, comprising:

a powder bed to receive a layer of an optically clear build material;

a first fusing agent applicator to dispense a fusing agent onto a first portion of the layer of the optically clear build material;

a second invisible fluorescence agent applicator to dispense an invisible fluorescence compound in an aqueous vehicle onto a second portion of the layer of the optically clear build material; and

an ultraviolet (UV) light source to emit UV light to fuse the first portion of the layer of the optically clear build material and the second portion of the layer of the optically clear build material.

13 . The three-dimensional printer of claim 12 , further comprising:

a processor to control movement of the powder bed to build each layer of a three-dimensional part that is to be printed, to control movement the first fusing agent applicator, to control movement the second invisible fluorescence agent applicator, and to control operation of the UV light source.

14 . The three-dimensional printer of claim 12 , wherein the invisible fluorescence compound is formulated with a UV absorber to act as a fusing agent, and the fusing agent dispensed onto the first portion of the layer of the optically clear build material is free of the invisible fluorescence compound.

15 . The three-dimensional printer of claim 12 , wherein the invisible fluorescence compound comprises Tinopal SFP.