I used those alphas to mask-select polygons on basic primitive 3D shapes such as cubes and cylinders. Then I deformed the polygons that were not masked. Here are some examples of the 3D tools I came up with by masking and deforming:
I did not use any texture for those. Their texture is just a tweaked material shader created by Jantim at ZbrushCentral.
Step 7:
After I had my library of objects, I placed them over my under painting, using the canvas Gyro tool, to push them back or pull them forward.
Step 8:
Here is my image with all of the 3D tools placed. Apart from lighting them with 3D lights, I also used the Intensity and the Highlighter brush to establish light and shadows.
