Germain I hope. From the 1933 "Modern Gunsmithing" by Clyde Baker. (A delightful book really.) Chapter 7, under sub-heading "A FEW SHOP KINKS", he states: "To distinguish between iron and steel, file the surface bright and apply a drop of pure nitric acid. After a minute or two, wash off with water. On wrought iron, the spot will be a pale ash gray; on steel a brownish black, and on cast iron a deep black."

As an aside, while I do not own anything with Damascus barrels, I have thoroughly enjoyed reading about the restorations and seeing the results can take one's breath away.