Gold toning is an intrinsic part of silver-based alternative processes, and has been used from the earliest times with printing-out paper (POP), as well as salt printing and kallitype to strengthen and permanise the image.
It does not, as one might think, give a gold colour, but deposits gold metal onto the silver of the image.
When used with enlarging papers, on an otherwise untoned print there will be a subtle enhancement, similar to the effect in selenium toning, but the shift will be to a bluish hue (above). Permanence will also be improved, although selenium has the edge on it in this respect. On a print that has been previously sepia toned, a range of colours from an orangey gold to a pink or rusty-red colour will be produced. This will depend upon paper and developer combination but also whether the sepia tone was more yellow or brown. A more yellowy sepia will tend to gold tone to a rich orangey or golden yellow (below) and a more brown sepia will tend towards red.
Images courtesy of Mike Crawford, Lighthouse Darkroom