2. Pale straw-color—450°. Still very hard, suitable for the faces of hammers and anvils. 3. Full yellow—470°. Shears and scissors. 4. Brown—490°. Gravers and turning-tools for hard metals; also percussion-lock gun tubes. 5. Brown, with purple spots—510°. Wood-working tools and most of the steel parts in a gun-lock with the exception of the springs; also knives of all sorts for cutting wood. 6. Purple—538°. Butcher-knives and other flesh-cutting implements. 7. Dark blue—550°. Tools requiring strong cutting-edges without extreme hardness, as case-knives. 8. Full blue—560°. Chopping-axes. 9. Grayish blue, verging on black—600°. Springs, saws, swords, and the like. Various other methods of tempering steel are sometimes recommended, as with oils, tallow, lead, mercury and divers solutions; but since the matter-of-fact gunsmith will find use for none of them, it is not deemed proper to encumber this book with anything further on the subject of tempering. It might be well to state, however, that the hardest degree to which steel can be brought is secured by heating the piece to a light yellow and instantly plunging it into cold mercury. _To Restore “Burnt” Steel._—Pulverize together two parts horn or hoof filings; one part sal ammoniac; one part charcoal, and one part common soda. When thoroughly ground together, work in tallow enough to make a kind of wax or paste. Bring the damaged steel to a bright cherry-red heat, and then cover with the paste, leaving it to cool gradually. The process may be repeated several times with profit if considered necessary. While a piece of badly-burnt steel may not be entirely restored by this process, it can be much improved. Entire restoration is scarcely possible. _Annealing Steel._—Heat the steel to a cherry-red in a charcoal fire, the last thing to be done before quitting work at the forge for the day or night; then smother the fire down with a thick layer of ashes or sawdust, leaving the steel in, just as heated. Let so remain until the fire is all out, and the steel entirely cool, which will require several hours. Some smiths use a piece of gas-pipe in which to heat small steel articles for annealing, claiming that it is very advantageous. They put the piece into the pipe and heat to a cherry red, looking in occasionally to ascertain when it has attained to that temperature; then they cover the fire, pipe and all, and leave it to cool as in the other case. _To Blue Steel._—Polish the article to be blued, then place it upon a strip of sheet iron and heat slowly over a forge fire or lamp, until the desired blue color appears. Let cool, and the color will remain permanent. _To Remove Blue Color from Steel._—Immerse for a few minutes in a liquid composed of equal parts muriatic acid and oil of vitriol. Rinse in pure water and rub dry with chamois skin or some kind of soft cloth.