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Watchmakers' Hand Book

Part II,
MATERIALS EMPLOYED IN HOROLOGY
Page 13

POLISHING MATERIALS.

      165. The following account of the materials used for polishing,is, for the most part, extracted from Holtspffel's Turning and Mechanical Manipulation, to which the reader is referred for fuller information to regard them, and to their mode of application:

      Buff' Leather glued to a flat surface, or to the edge of a revolving disc, is used with emery, crocus, rotten-stone and other powders.

      Charcoal is much used by steel and copper-plate engravers. That made by burning elder without access of air is considered the best, but willow and elm have also been recommended.

      Diamond, in the form of powder, is used by lapidaries, seal engravers, and watch jewel makers. The latter obtain the diamond bort that is rubbed off stones in faceting, and they separate it into various degrees of fineness, by decantation (168). The mode of applying it is described in articles (207, 216).

      Diamantine, Sapphirine, Rubitine, etc., are names given to various chemical preparations for polishing, to be obtained at the tool shops; they must not be assumed to consist in any way of the jewels from which their names are derived.

      Emery. At the present day, oilstone dust is very frequently replaced by emery with oil or water, especially in clockwork. Any required degree of fineness can be obtained by decantation. Emery dust is sometimes used in place of rouge for polishing.

      The solid emery wheels and sticks, that are now common in the trade, work rapidly, but they have the disadvantage of heating steel, and many of them soon become pasty. The heating renders them less suitable for grinding gravers, but they are very convenient for roughly shaping steel work, or removing the hard surface caused by the application of heat.

      To make emery paper. If occasion requires it, this can be done as follows; Fix a sheet of stout rope manilla paper on a board, gluing it round the edge. Having put emery powder into a sifter, the mesh of which has the requisite degree of fineness, and rapidly covered the surface of the paper with thin hot glue, shake the sifter lightly over the paper until it is evenly covered, and leave to cool. When dry, detach the paper and shake it vigorously to detach loose grains. Cloth may be used instead of paper, if desired.

      Hone slates. Under this heading are included a great variety of stones used for smoothing and polishing.

      Ayr-stone, or water of Ayr-stone, is much used for smoothing brass work prior to gilding (142), etc. It should be kept wet in order to prevent it from becoming hard.

      Blue polishing stone is much used by jewelers, clock-makers, and others; it is recommended for use in spotting (174) and for polishing wheels (176).

      Oilstone. This forms the quickest cutting whetstone known. Oilstone slips are used by watch-makers after the manner of files. Oilstone powder, or dust, is much used in the earlier stages of polishing, and is preferable to emery in that it does not leave particles embedded in the surface of the metal. On pewter laps it may also be employed for polishing steel work.

      Oxides of iron. Under this head are included the several materials known as crocus, rouge, red-stuff, colcothar of vitriol, etc. It is advisable to remove gritty particles from these materials by decantation (168) before using.

      Pumice Stone is extensively used for polishing cut glass, and is applicable to brass and other metal work.

      Putty Powder is oxide of tin, or, more commonly, of tin and lead in varying proportions. The whitest kind, provided it be heavy, is considered the best.

      Rottenstone. This variety of tripoli is of the greatest value for polishing brass work, as well as for silver, glass, and even the hardest stones.

      Tripoli is of a greyish yellow or red color, and consists mainly of silica. Its principal use is in the polishing of hard woods.

      Whiting is common chalk, ground, washed to remove sand, etc., and dried in lumps.

      166. Polishing stones. The following method is described by M. Cadot for preparing these stones, which are very useful for polishing a wheel that is not riveted to its pinion (see article 185).

      Carefully select a blue stone; after dressing its surface, smooth it with emery paper of gradually increasing fineness. Saturate the surface with oil, and rub it with a common piece of rough sapphire, one face of which is flat and partly smoothed, until the surface of the stone is hardened.

      Such a stone is used dry. The wheels must previously have been carefully smoothed, since the stone does not abrade the metal. If care is taken to avoid scratches, the surface will last for a long time, although, of course, it is only serviceable for gold, brass, nickel or metals of a similar degree of hardness.

      167. The several materials used for polishing must be kept carefully packed (glass stoppered bottles are preferable), as a few grains of dust, or of foreign bodies, will suffice to prevent the operation of polishing from being successful. Polishers should be filed very smooth, with a perfectly clean file that is not quite new. Files that are dirty or new will deposit small hard particles of dirt, or cause pieces off the point of their teeth to become embedded in the surface of the polisher.

PREPARATION OF POLISHING MATERIALS.

      168. Decantation. This consists in causing a material in a fine state of sub-division to fall slowly through a liquid with the view to separate coarse particles, or various degrees of fineness, by taking advantage of their different rates of descent.

Part II Fig 40

      The watchmaker should prepare all his smoothing and polishing materials, etc., by decantation. He will by this means obtain them in grains that are much more uniform in size, of any required degree of fineness and free from hard or large particles.

      The operation is exceedingly simple. The material having been pounded under the hammer or otherwise, is thrown into a vessel more or less filled with a liquid, water, oil, etc. After being thoroughly stirred, it is allowed to partially settle, and the liquid is carefully poured into another vessel. All the coarse heavy grains will be found as a residue in the first vessel; they are collected and used for coarse work. After again stirring and leaving to settle for a longer period, the liquid is again poured off, and the powder thus separated will be the second degree of fineness, so that it may be termed No. 2. By successive operations, in which a gradually increasing interval of time is allowed, Nos. 3, 4, etc., can be obtained; that is to say, a series of powders of the same material but presenting a greater degree of uniformity in the size of grains and of gradually increasing fineness. It may be observed that when the powder of the requisite degree of fineness is nearly attained the mass should be left to settle until the following day, or, rather, until the fluid is clear; then decant carefully so as not to lose any of the deposit.

      When treating a material that is soft and friable, it should be crushed between the fingers, as by using a hammer hard grains of foreign matter might be accidentally intermixed. Oil may be used for decanting diamond powder or oil-stone dust for smoothing; water for rotten-stone or tripoli; alcohol for hartshorn, etc.

      169. To prepare diamond powder. Select rough diamonds of a blackish tint, of such a size that there are four or five to a caret. These are crushed in a hard steel mortar of the form indicated in fig. 40, the pestle being provided with a small stuffing box that can be brought down on to the mortar to prevent the escape of diamond-dust; but it is well to first crush one stone, with a single blow of the hammer on the pestle; remove all the fragments and examine the end of the pestle; it will be found that a number of particles have bedded themselves in it; these should be examined to select pieces to serve as drills and gravers. The larger fragments serve for gravers, and particles should be sought that are as nearly as possibly triangular prisms about 1-50 inch long for making drills. The other stones may be treated in similar manner till enough fragments are found. Now place all other pieces in the mortar, and continue for two or three hours striking the pestle with the hammer, turning it partly round after each few blows to prevent the powder from imbedding itself in the steel. When no "bite" is perceived in rotating the pestle, the diamond is sufficiently reduced; it is shaken out of the mortar into a watch-glass containing the most limpid oil attainable, and if necessary the fragments are released by a steel spatula, at the same time striking the external surface of the mortar with the hammer. Thoroughly mix the oil and the powder, subdividing the latter as much as possible by rubbing against the glass with a spatula; allow the mixture to rest for an hour and pour off the liquid into a second glass, leaving the larger particles behind. Leave the oil in the second glass for four hours; then decant, into a third glass with the same precautions; this is left for eight hours; the next glass sixteen hours. When all the powder has settled pour off the oil, and the several degrees are ready for use.

      Some jewelers prefer to leave the powder for two or three days in a mixture of equal nitric and sulfuric acid in order to dissolve particles of steel. The acids are then much diluted with water, left for some days and decanted. Then wash the powder in two fluid ounces of pure alcohol, leave for two days, decant and dry, and afterwards treat with oil. The operation is long and hardly necessary.

     

Submitted by: Samuel Kirk (##)

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