BURNISHER. - This valuable instrument is in general a piece of hardened steel very highly polished, and when judiciously applied to the smooth surfaces of metals, it imparts to them, by means of friction, or intimate contact, a polish nearly equal to that which the burnisher itself possesses. 2. - The Action of the Burnisher appears to depend upon two circumstances; first, that the harder the material to be polished the greater lustre it will receive, and the burnisher is commonly made of hardened steel, which exceeds in hardness nearly every metallic body. And secondly, its action depends on the intimacy of the contact, betwixt the burnisher and the work; and the pressure of the brightened burnisher being, in reality, from its rounded or elliptical section, exerted upon only one mathematical fine or point of the work at a time, it acts with great pressure and in a manner distantly analogous to the steel die used in making coin; in which latter case, the dull but smooth blank, becomes instantly the bright and lustrous coin, in virtue of the intimate contact produced in the coining press, between the entire surface of the blank and that of the highly polished die.

It by no means follows however that the burnisher will produce highly finished surfaces, unless they have been previously rendered smooth, and proper for the application of this instrument; as a rough surface having any file marks or scratches, will exhibit the original defects, notwithstanding that they may be glossed over with the burnisher which follows every irregularity; and excessive pressure, which might be expected to correct the evil as in coining, only fills the work with furrows, or produces an irregular indented surface, which by workmen is said to he full of utters.

Therefore, the greater the degree of excellence that is required in burnished' works, the more carefully should they be smoothed before the application of the burnisher, and which should be cleaned on a buff stick with crocus immediately before use; and it should in general be applied with the least degree of friction that will suffice. Cutlers mostly consider that burnishers for steel are best rubbed on a buff stick with the finest flour emery; for silver however they polish the burnisher with crocus as usual. Most of the metals previously to their being burnished are rubbed with oil to lessen the risk of tearing or scratching them, but for gold and silver, the burnisher is commonly used dry, unless soap and water or skimmed milk are employed; and for brass furniture, water with or without a little vinegar, or else beer is preferred for lubricating the burnisher. 3. - The most General Forms of Burnishers. - The burnisher used by mechanicians generally, resembles in form a file of elliptical section without teeth; it is made particularly hard and well polished. For engravers in line and mezzotint, the burnishers are sometimes crooked like the horn of a cow; for watchmakers and others, they are flat so as to apply to pivots, and other burnishers for these artizans are nearly cylindrical for the interior surfaces of pivot holes, and which are applied as in using a polygonal broach. For ironmongery a narrow piece of steel is inlaid in a cross handle of wood, that is used almost like a spoke-shave, and the pressure is increased by a leather strap or bridle attached on both sides of the burnisher, in the bend of which the workman places his foot, to give the pressure. The same form of burnisher is employed in Sheffield for the springs of pocket knives, but the strap is generally omitted.

The burnisher is sometimes also fitted up with a handle at one end and a hook and staple at the other, somewhat like the paring knife used by clog makers and others (see fig. 18, vol. 1, page 26). This kind, which is called the clog burnisher, is much used at Sheffield, for the backs and squares of knife blades, which, after they have been made quite smooth, are moistened with the tongue and burnished with the clog burnisher, then the work and tool are wiped quite dry with a clean linen cloth, and a very gentle dry burnishing completes the work.

Fender makers and others have the burnisher at the bottom end of a pole suspended from the ceiling, or rather from a long and strong spring like that of the pole lathe, or a straight coach spring; this enables them to take a very long and equal stroke. The same contrivance, (which is also used in calendering cloth by hand,) is nearly copied, but with a piece of leather and emery, for laying a straight and dull grain on long works.

Burnishers made of flint, agate, and bloodstone are used by bookbinders and picture frame makers, also by silversmiths and jewellers, and other artizans, see Bloodstone.