A previous poster suggested bleaching and redeveloping in a staining developer. This process has worked well for me. I use the same kind of bleach that you would use for sepia toning a print and redevelop in PMK in room light to completion. The silver image is restored and a stained image is added. The process may be repeated. It is not well known that hydroquinone is a staining developer when used without sulfite. It is soluble in isopropanol. Mix Pyrocat-HD using hydroquinone instead of catechol, leaving out the bisulfite, and use it instead of PMK if you wish.