there are plenty of ways to blue metal i use a heat/oil bluing method though there are others such as cold bluing, hot bluing, Belgian bluing also know as hot water bluing. they all achieve the same general result (a rust proof beautiful finish) but my method tends to be the least durable but i find it brings the best variation of color depending on your amount of patience. With proper care the finish will last a long time (just coat it with alittle bit of gun oil every so often)