A Retractor is used in fading work on the rose engine lathe. Unlike a fixed fading mechanism (e.g., the MDF rose engine's fading wedge), a retractor can be used to change the fading during the cut.
How it works: a typical retractor is a screw mechanism that is rotated using some form of mechanical attachment to the spindle. A common approach is to use a belt drive so that, as the spindle rotates, it also drives the action of the retractor to turn the screw.
Artists who do fixed tool turning can use this to "ease into" the rosette's pattern. They will establish the height of the cut (the outside diameter) first, and then engage the retractor so that, as the piece rotates, the amount of fading will be steadily reduced, and the cutter will be engaged to cut deeper and deeper. The retractor allows this to be done much more easily and efficiently. (The alternative is to do this manually, and that is far more time consuming.)