How did people wash dishes before dish detergent?
When on a month-long kayaking trip back in the USSR, we did not bring dish detergent with us, so I have a peculiar opportunity to tell the history of soap from personal experience ;-). You scrub dishes with sand to remove hard residue (e.g., the burned food strongly attached to the walls of the pot).. You remove fat using ash (we cooked on open fire, so ash was plentiful).