This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
(1) Take an ordinary bar of malleable iron in its usual merchantable state, remove the oxide from its surface by the application of diluted sulphuric acid, after which wash the bar in an alkaline solution, then cover the entire bar with oil or petroleum. The bar is then ready for the chief process. A muffle surface is so prepared that a uniform, or nearly uniform, heat can be maintained within it, and in this furnace the bar is placed. Care must be taken that too great a heat is not imparted to it, for on this depends the success of the operation. When the bar approaches a red heat, and when the redness is just perceptible, it is a certain indication that the proper degree has been attained. The bar is then at once removed, and passed through the finishing rolls 5 or 6 times, when it will be found to have a dark polished uniform surface, and the appearance of Russian sheet iron.
(2) Keys, Key-rings, and other articles of iron. - ■ Finish them well with a dead smooth file, then mix some fine emery and oil together, hold the key in wood clangs, take some long strips of wash-leather, dip in the above, and polish well every part until all scars disappear; then tie 2 or 3 dozen on a piece of iron binding-wire, put them in an iron box with leather scraps burnt and made into a fine powder, cover bottom of box 1/2 in. thick, spread out the keys on this, cover them up with the powder or leather-dust, put a lid on, tie down, put in a slow fire until the box is red hot, soak about 20 minutes, then open the box, take out the keys quick, plunge them in oil - water makes them too brittle; now repeat the polishing as before, with long leather strings dipped in the oil and emery, until all the black from the "hardening " is off every part, then take them to the brushing-frame, charge your brush well with flour of emery, keep turning the key in every direction until the polish begins to appear; after this dip them in slaked lime, and get off every particle of grease. Take them to another brushing-frame, the brush charged with crocus and water; keep dipping the key in occasionally, and follow up process on the brush until the polish comes up well.
To put the extra gloss or polish on, take the leather strings as before, this time dipped in a mixture of putty-powder and water; work the string well over every part until dark polish comes up. If you wish a higher polish, it is done by hand - thatis, girls dip their hands in the putty-powder mixture above, and rub every possible part up with the palm of the hand, and this gives the beautiful polish that is upon them. (Aubin.) (3) Boden recommends the following method of brightening the surfaces of iron plates, wire, etc., as the result of numerous experiments made in the laboratory of the Industrial Museum at Munich : - The object, whatever it may be, just as it comes from the forge, is laid for the space of one hour in dilute sulphuric acid (1/20 part acid). The action of the acid may be increased by the addition of a little carbolic acid (?). The forge scales are loosened by the action of the acid, and the object is then washed clean with water, and dried with sawdust. Next, it is held for an instant in nitrous acid, the operator of course being on his guard against the nitrous fumes, washed again carefully, dried in sawdust, and rubbed over clean.
Iron goods thus treated acquire a perfectly bright, pure surface, having a white glance, without the intervention of any mechanical process of polishing.
(4) Steel. - Use bell-metal polishers for arbors, having first brought up the surface with oilstone dust and oil and soft steel polishers; for flat pieces use a piece of glass for the oilstone dust, a bell-metal block for the sharp red stuff, and a white metal block for the fine red stuff. The polishing stuff must be well mixed up and kept very clean; the polishers and blocks must be filed to clean off the old stuff, and then rubbed over with soft bread; put only a little red stuff on the block and keep working it until it is quite dry, the piece will then leave the block quite clean; use bread to clean off the surplus red stuff before using the brush. If the piece is scratched, put on some more red stuff, which must not be too wet, and try again.
(5) The polish on flat steel pieces in fine watchwork is produced with oilstone dust, burnt Turkey stone, and a steel polisher, soft steel, bell-metal, and sharp stuff, grain tin and glossing stuff. The metals are squared with a file, and vary in shape according to the work in hand.
(6) Get an 18-gal. barrel and put an iron spindle through the two ends; mount it on trestles in the same way as a butter churn, with a winch to turn it by; cut out a hole in the side by which to introduce the articles to be polished; have a tight-fitting cover to the hole; procure some worn-out casting pots or crucibles, such as used by casters, and pound them in an iron mortar, until fine enough to pass through a sieve which will not allow the steel articles to pass through. Put equal quantities of this grit and of the articles in the barrel; fasten on the cover, and turn the barrel for about an hour, at the rate of about 50 turns a minute; take all out of the barrel and sift out the grit. If a finer polish than this is required, put them through another turning, substituting for the grit small scraps of leather, called mosings, which can be procured from curriers, and emery flour. Do not more than half fill the barrel.