Set up a space in which to photograph the piece. Find a room that lets in as much natural lighting as possible. Take a dark piece of material, such as a sheet, tablecloth, or blanket, and tape the top of it to a wall. Allow it to fall, draping itself over the floor or flat surface beneath the wall.
Place your 3D piece on the drapery covered flat surface, directly in front of the draped wall.
If your work area is not well lit, set up a household lamp right beside the piece. This will help to emphasize the work's artistic features.
Photograph the work, with the flash off. Take multiple photographs to allow for many options in the end.
Select the best photographs of the piece. If just one does not do it justice, select two or three, each one featuring a different angle. This will give viewers of your portfolio the full impression of the piece.
Print the images off of a computer at home, or take them to a print shop. Print shops can print your photos to size, in order to fit your portfolio perfectly.
Place the images of the 3D piece into the art portfolio.