When I was first thinking about doing redwork, Simply quilts had a show on it. You can see how long ago that was. She said she uses a pencil it is covered by the time you are done anyway. I have used a pencil for all of mine. Don't use it too heavy it will show, but pencil works best for me. Then I took a old scanner I had bought at a thrift store, bought some cheap light strips to go inside took out all the insides and I have a light box. It was easy to do and not at all expensive.
Rita.