You need to overexpose the paper up to 3 stops, never underexpose.
Chemistry:
Paper developer, normal or thinner than usual
Rotes Blutlaugensalz, 40g/Liter water to bleach
Natriumsulfit, 90g/Liter water to clear
lightsource to flash the paper
Overexpose the photopaper up to 3 stops (if to dark, overexpose more)
Develop fully, paper will be rather dark.
short stop in water
Bleach. Minimum 2 min. When nothing more happens,
short stop in water
Clear. Minimum 2 min. Pic gets milky
Water Stop, put paper in with pic upside.
Flash paper: minimal flash or light. (if you do sepia or sulphur toning you do not need the flashing or the second development, the toner does work without these steps)
Second development, you can thin the developer 1:1.
5. Fix, long Waterbath
If pic isa to dark: In light bleach with 1:5 soluted bleach till the result is good and than stop in water. Again developing of the highlights in thin (1:10) developer, repeat if needed.
Another Fix and waterbath….
(This procedure was published from Rüdiger Hartung (great guy btw) in the facebook group Analoge Fotografie.)