Selenium toning was originally devised to increase print permanence and reduce fading. I wish i could remember how i did most of this.
This turned out really cool though.
Open the original image
Desaturate the duplicate with luminosity checked.
Now duplicate that desaturated layer 3 times.
You should now have 4 desaturated layers and the original.
Create 4 new transparent layers - 1 above each desaturated layer.
first layer color - 292524
second layer color -7c2849
third layer color - bab17a
fourth layer color - 6cbfe9
Place each color layer in overlay mode.
Now you have to turn off all but 2 layers at a time and merge visible.
merge 1 desaturated layer with it's color layer above it.
Then you will have 4 layers all merged and one original.
top layer mode - set to lighten only
2nd layer mode set to - Darken only
3rd layer mode set to - Value
4th and final layer mode set to - Lighten only
Original of course is set to normal mode on the bottom.
Save the image