6. Prepare your nitrate. Measure 1/4 cup (or 40 ml) of water for every 100 grams (3.5 oz) (about a 1/2 cup) of potassium nitrate in an old pan. Add your potassium nitrate. Bring to a boil. Stir continuously. Add little bits of water at intervals until the potassium nitrate is completely dissolved. 7.