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.
The burnishers used are of two kinds, of steel and of hard stone. They are either curved or straight, rounded or pointed, and made so as to suit the projecting parts, or the hollows of the piece. Stone burnishers are made of blood-stone, cut, and either rounded with the grindstone, or rubbed, so that they present, at the bottom, a very blunt edge, or sometimes a rounded surface. These are polished with emery, like steel burnishers, and are finished by being rubbed upon a leather, covered with crocus martis. The stone is mounted in a wooden handle, and firmly fixed by a copper ferrule, which encircles both the stone and the wood. The best blood-stones are those which contain the most iron, and which, when polished, present a steel colour. The operation of burnishing is very simple; take hold of the tool very near to the stone, and lean very hard with it on those parts which are to be burnished, causing it to glide by a backward and forward movement, without taking it off the piece. When it is requisite that the hand should pass over a large surface at once, without losing its point of support on the work-bench, in taking hold of the burnisher be careful to place it just underneath the little finger.
By this means the work is done quicker, and the tool is more solidly fixed in the hand. During the whole process, the tool must be continually moistened with black soapsuds. The water with which it is frequently wetted causes it to glide more easily over the work, prevents it from heating, and facilitates its action. The black soap, containing more alkali than the common soap, acts with greater strength in cleansing off any greasiness which might still remain on the surface; it also more readily detaches the spots which would spoil the beauty of the burnishing. In consequence of the friction the burnisher soon loses its bite, and slips over the surface of the article as if it were oily. In order to restore its action, it must be rubbed, from time to time, on the leather. The leather is fixed on a piece of hard wood, with shallow-furrows along it. There are generally two leathers - one made of sole leather and the other of buff leather. The first is impregnated with a little oil and crocus martis, and is particularly used for the blood-stone burnishers; the other has only a little putty of tin scattered in the furrows, and is intended exclusively for rubbing steel burnishers, as they are not so hard as the blood-stones. Blood-stone being very hard, the workman uses it whenever he can, in preference to the steel burnisher.
It is only in small articles, and in difficult places, that steel burnishers are used; as they, by their variety of form, are adapted to all kinds of work. In general, the blood-stone greatly reduces the labour. "When the articles, on account of their minuteness, or from any other cause, cannot be conveniently held in the hand, they are fixed in a convenient frame on the bench; but under all circumstances be very careful to manage the burnisher so as to leave untouched those parts of the work which are intended to remain dull. When, in burnishing an article which is plated or lined with silver, there is any place where the layer of precious metal is removed, restore it by silvering these places with a composition supplied by the silverer, which is applied with a brush, rubbing the part well, and wiping it afterwards with an old linen cloth. The burnishing being finished, remove the soapsuds which still adhere to the surface of the work; this is effected by rubbing it with a piece of old linen cloth. But when there are a great number of small pieces to finish, to throw them into soapsuds and dry them afterwards with sawdust is more expeditious.
The burnishing of gold leaf or silver, on wood, is performed with burnishers made of wolves' or dogs' teeth, or agates, mounted in iron or wooden handles. When about to burnish gold, applied on other metals, dip the blood-stone burnisher into vinegar; this kind being exclusively used for that purpose. But when burnishing leaf gold on prepared surfaces of wood, keep the stone, or teeth, perfectly dry. The burnisher used by leather gilders is a hard polished stone, mounted in a wooden handle - this is to sleek or smooth the leather. The ordinary engravers' burnisher is a blade of steel, made thin at one end, to fit into a small handle to hold it by. The part in the middle of the blade is rounded on the convex side, and is also a little curved. The rounded part must be well polished, and the tool be very hard. This burnisher is used to give the last polish to such parts of copper and steel plates as may have been accidentally scratched, or speckled, where false lines are to be removed, and also to lighten in a small degree such parts as have been too deeply etched or graved. In clockmaking, those pieces or parts are burnished which, on account of their size or form, cannot be conveniently polished.
The burnishers are of various forms and sizes; they are all made of cast steel, very hard, and well polished; some are formed like sage-leaf files, others like common files - the first are used to burnish screws and pieces of brass; the others are used for flat pieces. The clockmakers have also very small ones of this kind, to burnish their pivots - they are called pivot burnishers.