Ferric Chloride (FeCl3) is a dry chemical compound mixed with water to produce an etchant normally used to etch copper coated fibreglass circuit boards, it can be purchased at electronics supply houses like maplins in the UK, or radio shack. it can also be bought as a pre-mixed liquid. it etches not only brass and copper, but steel as well, and collectors use it to bring out the pattern of laminated or pattern welded steel, differentially hardened steel, damascus and wootz/bulat.