Potassium Sulfate (K2SO4) 1/2lb.

Potassium sulfate (K2SO4) (in British English potassium sulphate, also called sulphate of potash, arcanite, or archaically known as potash of sulfur) is a non-flammable white crystalline salt which is soluble in water. 

Patina Recipe: DESPIAU BLACK (Hot process):
Solution 1:
- Copper Nitrate (1 tsp.)
- Clean, potable water (1 pint)
Solution 2:
- Ferric Nitrate (1/2 tsp.)
- Clean, potable water (1 pint)
Solution 3:
- Ammonium Sulfide (1/2 tsp.)
- Ferric Nitrate (1/2 tsp.)
- Clean, potable water (1/2 pint)
Solution 4:
- Potassium Sulfate (1/2 tsp.)
- Ferric Nitrate (1/2 tsp.)
- Clean, potable water (1/2 pint)
Note:  Form a base patina with Solution #1, then add a light coat
of Solution #2, then apply Solution #3, then water, then Solution
#4, then water, then Solution #3...until desired intensity is
achieved.