Making potash involves taking ashes from dry, untreated wood and then separating it out with water. This process allows the 6 percent potash normally found in ashes to be extracted and distilled into a purer product.
First, fill a 2-liter bottle one-third of the way full of ashes. Fill the rest with hot water, place a lid on the bottle, and shake it up. Some insoluble particles settle at the bottom, and some charcoal floats to the top. Let it sit over night. The next day, uncap the bottle, and squeeze it to let the charcoal flow out. There are still two layers: the water and the insoluble solids. The potash is in the water portion.
Pour about a liter of the water, carefully so as not to release any sediment, into a non-aluminum pot or beaker that can be heated on the stove. Do not use aluminum because it reacts with strong bases, which would ruin the project. Once the water is poured into the heating container it can be brought to a boil. After the water has boiled out, a light grey powder is left. Collect this potash, and place it in a container for later use. PH test paper should turn blue if the potash is tested.