There is, properly speaking, only one kind of potash, and this is the oxide of ths metal potassium. The name potash was first applied to the ashes formed by burning plants, this being done in pots; after purification by dissolving in water, filtering, and evaporating to dryness, the product is known as pearlash, and is an impure kind of carbonate of potash. American potash is really a pearlash, and is used with vandyke brown for brown stains. The name potash is often applied to caustic potash. There are several salts of potash used for staining purposes; bichromate of potash is used for staining mahogany darker, chromate of potash yields a yellow stain, permanganate of potash a brown stain, and ferro-cyanide of potash (yellow prussiate) with an iron salt yields a blue stain.