Copied from JulieHRR from this thread:
Forums at Splitcoaststampers
Here is what she says:
There are a variety of ways . . .
1. Most widely known, is to use a large blank piece of a rubber type image--for example Great Shapes in the SU! catalog has a large flat rectangle shape.
Ink your stamp with pigment ink, and stamp it ONTO the large flat rectangle, then stamp (transfer) the image onto your paper by stamping the rectangle.
If you want to "mirror" that image, you can ink it up again (the focal image, not the rectangle), and then align and stamp it so the image appears to mirror itself, hence the "reverse" image effect.
#2. Ink stamp with pigment ink, and carefully roll rubber brayer to transfer image onto it, then brayer the image onto your paper. And, as in #1, re-ink the image,and align and stamp it so it appears to mirror the brayered image.
#3. Stamp with Staz-On onto acetate, flip the acetate over, and stamp the image again, aligning and stamping so it appears to mirror the original image, which is actually on the opposite side of the acetate.
Since I couldn't say it better I figured I would copy what she said here..lol