Hi Martin,
Dictionary of Photography (19th Ed.); Illife Books Ltd, London; Sowerby, A.L.M. (ed.); 1961, pp 657-658 has a formula for Platinum toning Printing Out Papers. I guess this would work on D.O.P.s, but I've been wrong before. Comments in brackets mine:
"This process gives very beautiful brown colours. First treat the prints in a 5 per cent solution of common salt (sodium chloride), rinse well and tone in:
Potassium chloroplatinite - 0.6 grammes;
Citric Acid - 8 grammes;
Water to - 880 c.c.
Wash thoroughly before fixing." (P.O.P. was traditionally toned before fixing.)
The text also lists two formulae for gold toning on p.654:
"The Ilford IT.5 formula is:
A. Thiocarbamide (Thiourea) 14 grammes;
Water to 1000 c.c.
B. Citric Acid (crystals) 14 grammes;
Water to 1000 c.c.
C. Gold Chloride 6 grammes;
Water to 1000 c.c.
For use, take 1 part each of A, B and C, and add to 10 parts of water. Chlorobromide prints benerally tone in 10 minutes or less; bromide prints take longer. Keep prints moving during toning and wash well afterwards.
Applied to a print already toned by any of the sulphide methods, gold toning gives a brilliant red-chalk colour. The Ilford IT.4 toner is:
Ammonium thiocyanate 20 grammes;
Gold chloride 1 gramme;
Water to 1000 c.c.
For a full red tone, about 10 minutes is normally needed. After toning, refix in 10 per cent hypo and wash fully".
Hope that's useful to you, have fun.