I've taken a couple of classes on redwork. One instructor had us use a very thin permanent marker (RED) (available at quilt shops or JoAnn's in my area) to trace the patterns. The two pieces of fabric really do help avoid the shadows.
Also, if you ever get a chance, try the Premium Sulky 300 mm, 100 percent cotton thread. It comes on a big spool, is machine washable or dry cleanable and comes in a beautiful dark red. It is a bit pricier than than DMC or whatever, but a spool goes a long way. I get it at one of our local quilt shops I have always hated separating out the different strands of embroidery thread. Silly, I know.