For a full refinish of a damaged finish, use fine metal finishing "sand paper". Lay a sheet on a flat surface, (use rubber cement to hold it down). Lay the slide or frame on the paper, and slide it across, and off the paper. You can't slide it back and forth, because this will leave circular scratches on the surface. If you take care to keep the surface flat, this will totally renew the finish.
To retouch a scratched or marred area, use a green or brown synthetic sandpaper subsitute pad, from most hardware stores, or a green "scratch" pad, available in most grocery stores. Simply rub the surface in long strokes, full length and off the end. Brownell's does (or did) sell stainless blending pads for this purpose, but I've found the green grocery store pads work very well.
The blending pad will restore the brushed or grained finish on non beadblasted stainless.