Well, at least for silver based Gelatine prints.
Following on from the last blog about toning there's another useful trick with traditional darkroom prints, that of toning by staining.
For aging and generally brownish effects, either a solution of tea or coffee can work wonders. These products stain black and white papers just as well as they stain our teeth....
For a variety of colours, food colourings can also be used. The sell-by date no longer matters as prints are not generally consumed, so any old colours will do. If we want to get slective about the colour, then varnishes can be applied to the parts of the print that we do not want to stain. After it is dry, the varnish protects the underlying black and white image. Afterwards, it can simply be peeled off.
This is one of the wonderful things about the darkroom monochrome print. It is a craft, a physical activity, and we can take the product and play with it to see what happens. We can also do exactly the same in Photoshop, but understanding the physical process does help us to visualise the sort of things that can be achieved. Don't try any of this with inkjet papers!