Chapter XIX: Part VI: Practical Recipes (3)

=578.= =To Polish the Cylinder Lips Mechanically.= The polishing of the lips of a cylinder is one of the most delicate operations that can be undertaken by a watchmaker; we have, therefore, endeavored to devise an instrument by which this can be done mechanically, and which should at the same time be so simple and so easily made that any watchmaker should be able to construct it for himself.

=579.= It consists of two distinct parts which take their place in an ordinary pair of finishing turns. 1. The plate P, Fig. 262, supported on a rod T, to take the place of the =T=-rest. 2. The frame E, whose axis replaces one of the runners. This much being clearly understood from the figure, there will be but little difficulty in understanding the following details.

On the plate P is mounted a bracket, _b b b′_, held by a screw and washer. It has a slot cut lengthwise, so that on loosening the screw it can be made to slide towards the right or left. The vertical portion _b′_ supports a fork-shaped piece, _d c_, a front view of which is given in Fig. 263, pivoted on a collet-screw, _f_, and this may be fixed by a pin passing through its end like a bolt. The upper end of the fork-piece is provided with teeth for a purpose that will be presently apparent.

The long spindle, _g h_, turns between the two supports, _k_, _l_, fixed to the plate P, under the action of the handle M. This axis carries two eccentric cams, _q_ and R. When it rotates, the eccentric R causes the fork _d c_ to rise and fall, thus occasioning an oscillating movement of the rack _d_, at the same time the other eccentric _q_ presses against the back of the slide _i n_, which moves freely in the guide _s_, and is always held against the cam by a helical spring _j_; the slide thus has an oscillating motion in the direction of its length.

All the details in regard to the slide and its guide will be easily gathered from the plan in Fig. 262, and the side elevation in Fig. 264.

A small iron polisher is adapted to the slide _n i_. Being pivoted on a pin at one extremity, serving as an axis, its end _u_ is pressed downward by the light spring _v_ (Figs. 262 and 264), which might be replaced by a spiral spring below the polisher if preferred.

=580.= This being understood, we will pass to the frame E.

The rod that carries it is formed of thick drawn steel pinion wire, the diameter of which is less than that of the hole in the poppet-head of the turns. This spindle is provided with brass collars at _y_ and _z_ of such an external diameter as to be received in the poppet-head, in which the rod can rotate freely. By adopting this arrangement, not only is the frictional surface diminished, without reducing the accuracy of the adjustment, but the apparatus can be easily adapted to any pair of turns.

To the right-hand side of the frame is fixed, by two screws, the cylinder carrier _x_ shown at X, Fig. 265. It must be removed in order to set the cylinder in position by cementing its balance to the surface; care is necessary to make sure that the back of the cylinder shall be towards the side _e_ of the frame when the carrier is again screwed in position. After having thus replaced it, set the rack _d_ to engage with the pinion wire _z_, in such a manner that, when the eccentric cam R occupies the position indicated in Fig. 263, the small iron polisher rests at the middle point of the cylinder lip. Now finally clamp the screw that fixes the support T.

The mode of action of the machine will be easily understood. If, after charging the polisher with polishing rouge the handle M is rotated, the cam R will impart an oscillating angular movement to the frame E through its axis _y z_, and the cam _q_ will, at the same time, cause the polisher to move backwards and forwards, always in contact with the surface of the lip during its movement.

=581.= The work will be performed more rapidly, and the polish will be better if the iron have a slight lateral motion as well as that in the direction of its length. It is, however, more simple to communicate a longitudinal oscillating movement to the cylinder, and this answers the same purpose; it is only necessary to make two small additions, the spiral spring _o_ and the little cock _a_. The latter is fixed to _d_ in an inclined position (as indicated at A), and this inclination can be varied by merely turning the left-hand screw. It will be evident that when _d_ is ascending, the cock will push the spindle _y z_ forward; and when _d_ descends, the spindle will be brought back to its initial position by the pressure of the spring _o_, which is simply placed over the end of the opposite runner. This longitudinal movement must be but slight, and it can be made as little as desired since it depends solely on the inclination of _a_.

=582.= _Observations._ 1. The angular motion of the frame E must be sufficient to enable the polisher to act on the entire surface of the lip. The extent of this movement is determined by the size and the degree of eccentricity of the cam R. The greatest motion will occur when the spindle passes through the hole 1 (Fig. 263), and it will gradually become less as the holes 2, 3, etc., are used. The cam _q_ should also have two or three holes for varying its eccentricity. These cams may be made of hard wood, ivory, etc.

2. The iron polisher may be replaced by a piece of flexible spring fixed by a screw to the slide; but its pressure is less uniform.

3. The bent arm _w_, Figs. 262 and 265, is clamped to the plate P by a screw _d_, and the long arm _b_, Fig. 265, bears against the back of the poppet-head, and thus ensures the steadiness of P. To insure steadiness by its means, _b_ is drawn back in the direction of the arrow, then hooked behind the poppet-head and clamped by the screw _d_. The firmer the support is the better.

4. The machine may be arranged so that the two lips can be polished at the same time, but it then becomes more complicated. In the tool here described, as soon as one lip is polished the cylinder carrier is unscrewed, turned around, and screwed against the left arm of the frame E, in which are two screw-holes opposite to those in the right-hand arm. Unscrewing the slide _b b_, the =T=-rest carrier is moved along the lathe bar until the polisher is over the lip; _b b_ having been set in position is clamped, and, after seeing that _w_ has a bearing, the second lip may be polished.

5. The cylinder carrier shown at X, Fig. 265, is used when the balance is in position. For a plain cylinder without its balance another form of carrier is employed that has at the edge of its central hole a small but solid projecting shell to which the cylinder is cemented.

=583.= _Methods of Obtaining Continuous Motion._ Rapid work is not possible when a single handle, as shown at M, is used for working the apparatus; recourse may, however, be had to one of the following methods:

1. Mount a small pinion with a square hole at its center, and make it engage with a large wheel driven by a handle. This wheel, having a great number of teeth, will proportionately increase the rate of motion.

2. Take a powerful clock movement and connect up its center arbor with the axis _g h_; having wound up the main spring, allow it to run down so long as it possesses sufficient power to drive the mechanism.

3. Fix a ferule at _h_, and drive it by the aid of a foot-wheel.

BALANCE SPRING.

=584.= =To Select a Balance Spring.= Various methods are adopted for this purpose. The most common, by which the strength is ascertained from the length of cone formed by hanging the balance from the inner coil of the spring while the outer is held in a pair of tweezers. A more exact method, based on the same principle, is to employ the small gauge shown in Fig. 266.

A vertical pillar _n n_ is fixed on a smooth plate B, and the slide C is held by friction in any position on _n n_. Place C so that the distance between _c′_ and B is equal to the distance between the end of the lower balance-staff pivot and the balance-spring collet. Having now fitted the spring in this collet, raise the balance, by tweezers holding the outer coil, until the lower pivot just rests on B. The graduations on C will then afford a measure of the extension of the spring, and this extension should about equal the radius of the balance measured on the same scale.

When the number of vibrations performed in an hour is known, a spring may be selected by fitting it to the balance and, while holding the outer coils in the tweezers, supporting the lower pivot on a hard smooth surface; the balance is then made to vibrate and the vibrations are counted. The spring need not be pinned into the collet, but may be attached by wax to the top pivot.

=585.= =To Fix a Balance-Spring to its Collet.= A common way of doing this is to put the collet on a wire or broach which is held in one hand while the other presents the inner end of the spring, held in tweezers, to the hole in the collet; subsequently fixing it with a pin. The following is a more convenient method:

At the middle of a brass plate is a boss tapped through a vertical hole in its center to receive a small screw with flat head. When the collet is fixed by this screw passing through it, the operation of setting the spring in position and pinning it will be much facilitated, and the plate will at the same time afford a means of testing its parallelism. Two or three screws with heads of various sizes should be provided, and, in order that they may be always available, they should be screwed into holes at a corner of the plate.

This tool might be made of further use by adding an arrangement for holding the stud while drilling it, with a view to ensure that the hole is at the proper height.

=586.= =Balance-Spring Gauge.= A back view and side elevation of this are shown in Fig. 267; it can be made without difficulty by any watchmaker.

Through the middle of the plate passes a staff _a b_ lightly pivoted between the cock _p_ and the plate, and projecting on the left-hand side as far as the point _a_. Between the cock and plate it carries the collet of the spiral spring _s_ and the stop-finger _d c_, and at the point _z_ is a light finger _y z_ that passes over the graduations on the dial.

When the stop-finger _d c_ is free it stands in the direction of the dotted line _i_; on rotating the staff, by taking hold of the pivot _a_, in the direction of the arrow _i_, the extremity _c_ of the finger will be brought round till it presses against the inclined plane _r_, which it will force back and, on coming against the stop near _c_, it will be held fast in the notch of the small bent lever that terminates at _r_. A spring maintains this lever always against a pin set in the plate. The index finger _y z_ will now be standing over the zero of the scale, and will be maintained in that position until the finger _d c_ is released by a momentary pressure of the hand on the push-piece _n_, when it will fly back to the initial position corresponding to the dotted line _i_.

=587.= The instrument is used as follows: The small sliding holder H, which is shown in section at E, (both of these figures being much enlarged since it is extremely fine and light), has a hole through its center that fits on to the axis at _a_. Having set a balance spring in the clip as indicated at E, place H on the pivot _a_, tightening the slide so that it can be used to rotate _a b_, and bring the stop-finger round to the position _d c_. Holding the outer coil of the spring in tweezers at _v_, its inner coil being held in the clip, release the bent arm by means of the push-piece _n_. The point on the dial at which the finger _y z_ is arrested will give a measure of the force of the balance spring _v_.

It will be evident that a spring can now be easily selected of the same strength as _v_, or stronger or weaker within definite limits which will become well known when some use has been made of the instrument.

The entire mechanism is enclosed within a box that is covered by a glass, through the middle of which a hole is made for the passage of _a_. The spring _s_ is of about the strength ordinarily used for 18-line watches.

=588.= =To Set a Breguet Spring in Position.= To test the strength of a flat spiral spring that is to be formed into a Breguet spring, it must first be attached by its collet to the balance-staff. As the outer coil cannot be held in the stud owing to its being so near to the pivot hole, it must be held in the clip _b_ of the little appliance shown at S, Fig. 268. Holding the watch-plate between _a_ and _c_, the arm D can rise or fall on the rod _h_, and _b_ can be brought to such a position that it grips the spring at a point just beyond the stud, so that, when the spring is turned inward, the point held may be brought up to the stud. The springing of the watch can thus be proceeded with, and springs tried until one of the required strength is obtained. It then only remains to give the spring the double curvature, and to take care that the end of the overcoil is brought sufficiently near to the center.

Since the action of a Breguet spring is more free than that of an ordinary flat spring, the watch may be found to lose slightly; it is advisable therefore to time the watch before making the bend, so as to show a gain. A little experience will enable the watchmaker to avoid being much out, and any trifling error that there may be is corrected either by a displacement of bend or by altering the central coil. If the latter method is to be resorted to, it is better that the watch should lose rather than gain a little.

=589.= =To Flatten an Ordinary Balance Spring.= Remove the collet and stud, and clamp the spring by a central screw between two plates, which are then placed on a blueing tray and gently heated. A small piece of whitened steel is laid on the plate in order to see that the heat does not exceed what is needed to give a blue temper. Allow the plates to cool and separate them.

Ordinary springs being made of rolled steel and subsequently coiled, always open out on heating; it is therefore necessary before resorting to the above method, to coil up the spring, as otherwise the outer turn will be found to have opened beyond the stud.

=590.= =To Diminish the Strength of a Balance Spring.= Scraping the end or the entire length always renders the spring defective. Dipping in acid is very little better. It is preferable to embed the spring in cork or soft pith, and work it over a ground glass plate covered with oil stone dust that is fine and smooth. This method might be resorted to for reducing the height of a mainspring.

If the cork or pith is hard and only a little metal has to be removed, the operation is successful; but it is apt to result in more metal being removed from the edges than from the center. When much has to be removed, the spring must be cemented to the polishing plate (shown at G, Fig. 269, and described in article =345=) with fine wax, thoroughly liquid, so that on pressing the spring all its coils may come in contact with the plate; it must be held thus until cold. Now adjust the leveling screws, so that the whole surface bears flat on the glass; rub it as long as is considered necessary, and detach the spring as soon as the plate is sufficiently heated; boil in alcohol to clean its surface.

=591.= =To Harden Gold Springs.= Gold detent, thermometer, suspension and balance-springs can be obtained of a high degree of elasticity. Rolling hardens them, but renders them very brittle. They can be made supple and elastic, not by hardening, as in the case of steel, but by annealing, care being taken not to exceed a certain degree of heat. The spring may be coiled on a block and placed in a tube that has a smooth steel lid, then heat the tube in the flame of a spirit lamp, and as soon as the steel is of a blue temper, remove the flame and allow the whole to cool.

Others anneal by keeping the spring in boiling oil for a definite period.

The hardness of a gold spring increases with the proportions of alloy it contains, and, if well annealed, it will be very elastic and will break when bent too far, as in the case of steel.

=592.= =To Ease an Index on Its Endstone Cap.= It is a common but bad practice among watchmakers to scrape the inside of the ring of the index or to cut it through. A better method is as follows: Resting the index on a cork, cover the inside of its ring with oil stone dust and make the cap rotate in its seat by means of a pinion calliper, the two points of which are inserted in the screw-holes. The operation is repeated as often as may be required.

DIAL PLATE.

=593.= =To Cut the Large Hole in the Timepiece Dial Plate.= Some workmen cut the hole in the dial-plate of a timepiece by means of a strong pair of compasses, one leg of which terminates in a bullet-nose that is supported in a central hole, while the other is provided with a hardened cutting point that serves to scrape out a groove.

Others use a rule that revolves on a conical point and carries a slide with a tracing point which can be replaced by a sharp-pointed cutter. Proceed in exactly the same manner as when using the compass, but a greater force can be applied, because, while one hand steadies the center, the full force of the other is applied to the cutter.

A third and still simpler plan is adopted by some clockmakers. A rod of the diameter of the central hole, and a cutter of which only the cutting point projects, are gripped in a vise at a distance apart equal to the radius of the hole to be made. Then passing the rod through the central hole and holding the plate in both hands, rotate it, at the same time applying pressure so as to cause the cutter to form a groove. When a moderate depth has been attained, invert the plate and cut one on the opposite side. Care is necessary when the grooves are on the point of uniting; on the removal of the center, smooth the edge with a half round file. Some workmen consider it more convenient to set the cutter and rod in a thick piece of wood that is rounded at the top and made flat on its two sides towards the bottom, so as to be firmly held in the vise.

=594.= =To Drill an Enamel Dial.= Take a hard, well-sharpened graver and moisten it with turpentine or turpentine that contains camphor in solution, or in the following mixture, which is still better:

Turpentine 62 parts by weight.
Oxalate of potassium 4 ” ”
Camphor 4 ” ”

The two latter substances are reduced to powder and dissolved in the turpentine, and two parts by weight of sandal wood may be added.

The graver point is placed on the dial at the point at which a hole is required and the graver is rotated backwards and forwards between the fingers. Practice, acquired by drilling a few holes in broken dials, will soon indicate the degree of pressure that can be applied without fear of accident. Some workmen prefer only to apply the maximum pressure while the graver rotates in one direction, reducing it during the opposite movement; others hold the handle or tang in one hand and rotate the graver with the other, always in the same direction.

The operation is continued, frequently arresting it, however, in order to set the graver and moisten it, until the copper-plate and back enamel are perforated.

As soon as this point is reached, take an iron or steel spindle, pointed at one end. The point must be more obtuse than the hole already formed in the dial. Charge this end with emery or oilstone dust, and place in the chuck in your lathe; when the spindle is caused to revolve the enamel on the contour of the hole will be rapidly removed. When the copper disc is reached, a fine-pointed and sharp graver must be used to remove the metal that is exposed as well as that which is covered with only a thin layer of enamel; then renew the operation with the spindle, occasionally drawing a file along the surface of the acting cone. Or the cones of solid emery to be obtained at material stores can be used for this purpose. A workman must be very careless or unskilful to fail in rapidly drilling a hole in a dial by this method without accident, and he may carry on the process easily until the hole is large enough to permit the introduction of a rat-tail file.

=595.= =To Enlarge a Dial-Hole With a Rat-Tail File.= As an extra precaution the contour of the hole on either side may be coned with a spindle as explained above, so as to reduce the thickness of enamel to be acted upon by the file; but a watchmaker that has had any experience can dispense with such a preliminary, which we would at the same time recommend.

The file must enter the hole freely. If only the point can do this, the file must be held very short, so that the finger may come in contact with the dial before the larger diameter of the file locks in the hole, as this would almost certainly crack the enamel. Some workmen avoid such an accident by forcing on to the file a rather long cork of small diameter.

With a view to avoid scratching the face of the dial in case the file is drawn out of the hole in its backward movement, it is well to round off and polish its point.

During the forward movement a slight circular motion is given to the file, and in returning no pressure is to be applied; the file must merely slide over the surface. It is dipped from time to time in the liquid mentioned in the last article. When the hole is large enough, a conical spindle should be used to smooth its edges as in the earlier stages of the process.

=596.= =To Remove Enamel from the Back.= To remove portions of the enamel from the back when it touches part of the motion work, etc., various methods are adopted.

The little spindles of solid emery that may be obtained at material stores may be used for the purpose.

Some watchmakers use a flattened lead ball perforated at its center and carried on a taper arbor, forming a kind of small grindstone, rounded across its rim. The arbor is held in a chuck and the edge of the lead disc is moistened with water, and emery powder sprinkled over it; when set in rotation the surface to be removed is held against the lead, the necessary pressure being applied by the finger against the other face. Water must be frequently sprinkled on the surface so as to avoid heating, and to maintain the emery in its place, and the dial is washed occasionally to examine the progress of the work.

In place of lead, some use emery formed into a solid block with shellac or various kinds of cement; it is centered on a large taper arbor, and should be at least a quarter of an inch thick and rounded at its edge. Such a disc is very hard when cold; it is used in the manner explained in the last paragraph, but wears more rapidly than the lead disc, if the latter is well made and supplied with emery of the right degree of coarseness, in sufficient abundance and evenly distributed.

=597.= =Dials Fixed by Screws through the Edges.= The screw-holes at the edge are drilled in the manner already explained in article =594=, and the center hole is enlarged as there described, if this is found to be necessary in order to permit the free passage of the hour wheel. The diameter of a dial may be reduced if it is too large in the manner explained in article =600=. When it has been thus prepared, place it in position, the XII being exactly opposite the pendant, with the movement in the case, and close the bezel. If the dial is found to shake under the bezel it should be fixed with three or four small wedges of pegwood, care being taken that they do not subject the dial to much pressure. The accuracy of the position may be tested by holding a stretched piece of cord over the dial, and observing whether it passes at the same time through the middle of the pendant, the center hole, the XII and the VI. When the dial is thus found to be properly placed, mark one of screw-holes on the watch-plate through a dial-hole. Some care is necessary in doing this lest the hole is marked eccentrically or the dial is displaced by pressure against one side of the hole in it, which might result in the dial being cracked by the screw. Now remove the plate from its case and drill its screw hole in the drilling tool; tap it and fit the screw. Replace the plate in the case, and, after fixing the dial to it with the one screw thus fitted, carefully mark the second hole, etc.

Some workmen expedite the operation by marking and drilling the two holes at the same time; but if at first they do not succeed in making them in the required position they materially increase the time occupied, as one hole at least requires to be bushed, etc.

=598.= =Dials Held in Position by Feet.= If the dial has feet, and it is required to adapt them to the plate, they must be first carefully bent straight; then take a piece of stiff card board of moderate thickness, and laying it on a piece of lead, punch out with a sharp-edged punch, or other means, a round hole of the diameter of a foot. Having inserted one foot in this hole, and placed the card on a flat surface with the dial uppermost, apply a slight pressure to this latter so as to mark the position of the second foot. Then punch out a second similar hole at the point thus indicated. If the operation has been properly conducted the two feet will enter the holes easily, but at the same time without constraint or shake, and they should project on the opposite side.

It now only remains to cut out the cardboard to the size of the plate, and, after making a central hole and a mark to exactly correspond with noon, to place it in position in the frame and under the bezel, as though it were the actual dial. Then mark the two holes for the dial feet, using a sharp-pointed chamferer that just fits the hole, held vertical and rotated by one hand, while pressure is applied by a finger of the other hand.

Some workmen merely prick holes in the card with some sharp-pointed instrument, or even force the feet through it at all risks; hence it happens that feet are often bent out of the vertical, and, in order to be able to bend them into the required position, it becomes necessary to enlarge the holes in the plate and bend the dial feet.

=599.= =To Cut a Large Hole in a Dial. To set a Seconds Dial.= This operation is performed in the ordinary lathe. The hole is cut by a ring of thin iron or copper cut with saw-like teeth round its edge, as shown at V, Fig. 270, kept in rotation and charged with fine emery and oil or water or, what is better, turpentine. The mixture described in article =594= will secure a still more rapid action.

It is advisable that the thickness of the ring be made to gradually diminish from _e_ towards _i_, as indicated by the section at S, so as to prevent it from choking and probably cracking the dial.

The following arrangement may be adopted: Prepare a strong ring with a projecting internal ridge, shown in section at A B C; cement the dial, _g d_, to this ridge, or fix it by any convenient means, and attach this supporting ring to a chuck that rotates in a direction opposite to that of the cutter, but much less rapidly. On reaching the copper disc, reverse A B C and repeat the above process on the back enamel. The copper is thus exposed on the two sides. On filling the deeper groove with dilute nitric acid the metal will gradually be eaten away, and the acid should be renewed as often as may be needed. It then only remains to smooth the edge, beveling it on the front side, and to cement the seconds dial in position.

The use of acid may be avoided and the cutter passed through the copper, but greater care must be exercised, because the work is more difficult when operating on metal. It will, however, not be difficult after a few trials.

Willis recommends that the dial be cut straight through, commencing at the back and using emery and oil, the dial being cemented on a brass block immediately below the cutter, and rather less in diameter than the hole produced. He mounts the cutter on a stock that is provided with a pump center, the point of which is maintained throughout the operation in the small hole or point that marks the center of the hole. The great advantage of this method is that the taper of the hole is in the required direction and no filing is necessary.

=600.= =To Reduce the Diameter of a Dial.= Resting the dial in an inclined position against a block, file its edge with a smooth or half-smooth file, which must only be allowed to act while advancing, and is at the same time displaced sideways and turned so as to follow the contour of the dial. The file should be dipped occasionally in turpentine, and when sufficient enamel has been removed, pass a new emery stick over it to remove the file marks.

=601.= =To Remove a Figure or Name from a Dial.= Oil of spike lavender may be employed for erasing a letter or number.

Enamel powder made into a paste with water, oil, or turpentine, is also used for this purpose. It should be previously decanted so as to obtain several degrees of fineness. The powder used for re-polishing the surface where an impression has been removed must be extremely fine. It is applied on a piece of pegwood, although some use ivory.

The last and best system is to use diamond powder. Take a little of the powder, made into a paste with fine oil, on the end of a copper polisher, the surface of which has been freshly filed and slightly rounded. On rubbing the marks they will be seen to rapidly disappear.

The surface is left a little dull; it may be rendered bright by rubbing with the same powder mixed with a greater quantity of oil and applied with a stick of pegwood.

Watchmakers will do well to try several degrees of fineness of the diamond powder on old dials.

METAL DIALS.

=602.= =To Restore a Silver Dial.= We proceed to describe several methods of doing this, but would at once observe that when the earlier ones are adopted, the hours, if they are painted, necessarily disappear; whereas they can be retained by resorting to the last method although great caution must in that case be taken; moreover, it is much more difficult to accomplish than the others.

=603.= First Method. This is the most expeditious system, and at the same time the most certain of success.

If the hours are in enamel, there need be no fear; if engraved and filled with black composition, this will disappear, but it can be replaced without difficulty. There remains the case of painted hours to be considered.

First make thin marks with a fine point along the lines of all the figures, taking care not to pass beyond their ends: and do the same for the dots and lines that indicate the seconds. By using a glass and following the instructions given in article =619=, no difficulty will be experienced in doing this, and the fine lines and dots thus made will afford sufficient guide for re-marking the hours.

Begin by cleaning the dial with a brush and fine pumice-stone so as to remove spots and slight scratches.

=604.= _To Frost the Surface._ In order to frost the surface of the dial, take a spirit lamp with large wick, and direct a blow-pipe flame from it against the under side of the dial, which is held by one hand with a hooked support. If the flame is gently directed over the entire surface of the back, a good dead surface is obtained that resists a moderate degree of friction either in soaping with a fine sponge, or washing in a large quantity of water, or in applying soft bread and oil of spike lavender to erase irregularities or marks made in painting the figures.

The application of the flame is several times repeated, so as to obtain a decisive and even frosting; but it is necessary, with a view to avoid buckling the thin metal, to place an iron or copper washer behind the dial. The flame oxidizes the surface of the metal; that is to say, it causes the oxygen of the air to combine with the copper which is alloyed with silver.

=605.= _Pickling or Bleaching the Dial._ Introduce sufficient warm water into a suitable flat vessel to completely cover the dial, and gently pour into it a few drops of sulphuric acid (oil of vitriol), so that the two liquids are in the proportion of about 1 to 10; then lay the dial in this dilute acid for a period that varies from half to one or two minutes. The frosting will first become yellow and then of a beautiful white color. Wash it in a large quantity of water, wipe with a fine linen rag, and apply the flame momentarily to the back in order to prevent the formation of spots on the surface.

When several dials have to be operated upon, the acid is put in a porcelain dish and boiled by a lamp. Then place each dial for a moment in it, wash in an abundant suppl of water, and dry by tapping with a fine linen rag.

=606.= Second Method. For the benefit of such as care to experiment with it, we add the following method: Brush the dial with a coarse brush and pumice-stone reduced to an impalpable powder until no scratches are visible. Make it red-hot and allow to cool. Then dip for two or three seconds in a porcelain vessel containing dilute sulphuric acid; on removal it will be found to be white, but rather dull. In order to produce a clear frosted surface, place the dial in a mixture of

6 parts by weight of nitric acid of 1.22 sp. gr.[8]
21 ” ” sulphuric acid.
50 ” ” water.

Allow the metal to remain in this acid until no more globules are seen to form on its surface, then withdraw it and immediately place in cold water. The dial will be observed to be nearly black; it is then pickled as above explained (=605=), washed well, heated red-hot and, when cold, again pickled; the operation is concluded by thoroughly washing its surface.

=607.= _Third Method._[9] Cover the surface of the dial with a thin layer of soap, and brush it over, taking care to avoid touching the hours if these are not enamelled. This can best be done with a fine brush and pumice stone reduced to an impalpable powder. When the dial has been made as clean as possible by this means, wash it carefully with water and tartrate of potash (cream of tartar), then plunge it immediately in the hot solution of nitrate of silver (=608=) attaching it to the silver wire which is fastened to the zinc and copper discs =609=; in two or three minutes the surface of the metal will be perfectly frosted, and, if each operation has been cautiously performed, the hours will remain intact.

Each time the zinc and copper discs are used they should be cleaned with nitric acid, and rubbed over with pumice stone. As soon as the dial is clean, immerse it in the solution; the least delay is apt to cause the surface to become oxidized through contact with the air.

=608.= _To Prepare the Silver Solution._ Dissolve an ounce[10] of solid nitrate of silver (lunar caustic) in a small quantity of water; filter the solution and add twice its volume of liquid ammonia. In a separate vessel dissolve 6 ounces of yellow prussiate of potash and 4 ounces of crystallized carbonate of soda in 60 ounces of water, contained in a vessel of enamelled iron, which must be placed on the fire. When near the boiling point add the concentrated solution of nitrate of silver, and allow the mixture to boil for an hour, taking care to add hot water in sufficient quantity to make up for that lost by evaporation; then filter the resulting solution.

=609.= _To Prepare the Discs and to Plate._ In order to use this solution for restoring a dial or plating any other object, take two discs about the size of a half dollar, one made of zinc and the other of copper, and, after making a small hole in each, unite them with a copper wire, or, preferably, with one of silver. After having attached the dial or other object to this connecting wire, immerse the entire system in a glass or earthenware vessel, and pour over it a sufficient quantity of the solution, previously made hot.

If the object operated upon is perfectly clean, bright and free from all greasy or oily matter, its surface will be found in two or three minutes to be covered with a firmly adherent layer of silver. When only a small piece is treated it will suffice to immerse it in the hot liquor, and rub it with the finger; a bright silvered surface will thus be obtained.

=610.= =To Clean Metal Dials of Clocks.= When the hours are neither enamelled nor engraved, it is necessary to first trace out the several lines and dots in a manner similar to that explained in article =619=.

=611.= _Ordinary Mode of Cleaning the Dial._ Very often it is possible to make a silver or plated dial of either watch or clock sufficiently clean by merely brushing with powdered cream of tartar worked into a paste with water, carefully rubbing around any painted figures with a fine stiff brush. Then wash with clean water, dry by gently tapping with a fine linen rag, and expose to a slight heat. (This is in part the same method as is described in article =607=; the two may be combined). If the dial is tarnished, it must be silvered as explained below.

=612.= =To Plate a Brass Dial.= _Preparing the Silver._ Place in a glass flask from 100 to 150 grains of pure silver made into thin strips by means of a hammer or rolling mill. Add five or six times the weight of dilute nitric acid so as to completely cover the silver, and warm the vessel, taking care to avoid breathing the fumes or admitting them to the workshop. The metal will be dissolved, and, on continuing the application of heat until all the liquid is evaporated, crystals will be found at the bottom. When cool fill the flask with warm water and, as soon as all the crystals are dissolved, pour the solution into a porcelain dish, previously half filled with water. Place in it a sheet of clean copper of about the size of three fingers, and allow it to remain for the night.

On the following day all the silver will be found attached to the plate, and it can be collected by immersing this in water. Carefully pour off the water from the fine powder thus obtained, and wash it once or twice with an abundant supply of pure water; then dry thoroughly with the application of very moderate heat. If the silver thus obtained is not required for immediate use, it should be kept in a dark blue bottle to avoid the influence of light and moisture.

=613.= _To Prepare the Surface of the Dial._ It must be quite smooth, thoroughly washed and dried. M. Robert recommends that the smoothing be accomplished by using soft water of Ayr stone, rubbing in all directions, in order remove scratches. Or pegwood charcoal can be used, sloped at one end like a whistle, and applied with water. Others employ pumice-stone powder and very fine emery paper.

=614.= _To Apply the Silver._ Take equal parts of rock-salt and cream of tartar, pound them together, and when well mixed, take about 60 or 80 grains of the mixture, and add to it 15 or 20 grains of silver, prepared as above described, and add a few drops of water to form a thick paste, which must be well mixed and worked up on a ground glass plate by means of a horn spatula to remove all grits. A glass pestle may be used for this purpose.

The dial having been prepared, take up some of the paste with a perfectly clean and rather stiff brush, and spread it over the surface of the dial, rubbing quickly and somewhat harshly. The brush should be worked about in all directions, so as to avoid scratches, until the silver is found to adhere firmly to the dial. According to M. Robert, this rubbing is to be continued until the required grain is obtained; but M. Fournier states that it should be arrested when the surface possesses a lead-grey color; the dial is then well washed, dried, and the operation re-commenced exactly as before except that the brush used is softer. A good surface will thus be formed, and it will be whiter if the proportion of silver in the paste is increased.

The result attained in great part depends on the skill of the operator, and this can only be acquired by experience.

=615.= _Observations._ If the mixture contains too much of the salt or too little silver, the latter will adhere with difficulty, and will come off in lumps or scales; moreover, it will not have so white a color.

As the proportion of silver is increased, the white becomes gradually better; but, on the other hand, if it is in excess the surface will be coarse and uneven. Too much or too little water will have nearly the same effect. The color is worse if the dial has been imperfectly smoothed, and when several days or even hours are allowed to elapse between the cleaning and silvering.

It is essential that the rock-salt and the cream of tartar be perfectly pure; if they contain any earthy matter it will scratch the surface and impair its whiteness.

As soon as the operation is completed, the dial must be washed in an abundant supply of pure water; any neglect in this particular will cause it to blacken. This washing may be performed with an ordinary watch-brush, charged with cream of tartar. Then rinse the dial, and dry, tapping gently with a fine linen rag, and finish by slightly warming it.

=616.= =Gold Dials.= It will not be necessary to say much on this subject. In order to restore the color to a gold or gilt dial, it may be dipped for a few seconds in the following mixture: Half an ounce of cyanide of potassium is dissolved in a quart of hot water, and two ounces of strong ammonia mixed with half an ounce of spirits of wine and added to the solution. On removal from this bath, the dial is immediately immersed in warm water; then brush with soap, rinse, and dry in hot boxwood dust. Or it may be simply immersed in dilute nitric acid, but in that case any painted figures will be destroyed.

=617.= _Another Receipt._ The following is the method ordinarily adopted for coloring gold dials; but it is to be observed at the outset that, although apparently characterized by extreme simplicity, a good deal of skill is needed to ascertain when the mixture is of the right consistency, and when the dial has been sufficiently exposed to its action.

Make a mixture of 4 oz. saltpetre, 2 oz. alum and 2 oz. common salt (the purest attainable), with a very little water. On placing this in a blacklead crucible over the fire it will become limpid, and must be allowed to boil until somewhat pasty and of a pale yellow color, stirring all the while with a stick. Now take two dials, back to back, that have been cleaned and blackened by annealing, and pass a platinum wire through their centers so that they hang horizontally, resting on a loop at its end; immerse the dials in the hot color crucible, and, after holding it for a short time, withdraw them and immediately immerse in a vessel of nearly boiling water standing close by. The “color” will then be washed, and the progress of the work can be observed. The dials are again dipped in the crucible if necessary, and will probably require about three minutes’ immersion in all. It is advisable that the “color” be thick rather than thin, as in the latter case the dials are apt to be clouded.

=618.= =To Re-Paint the Hours on a Dial.= The following system has reference to metallic dials, but the reader will be able to select without difficulty the parts that are applicable to altering and retouching the figures on an enamel dial.

We can answer from experience for its being successful, but would at once observe that it cannot be practised hastily, because some skill is essential in addition to patience and care: with them, success is certain.

=619.= _First Method._ Before removing the hour figures and the divisions for minutes, mark them with a fine steel point, using a lens and proceeding with great caution. These marks will remain, so that after the dial has been colored or otherwise treated, it will only be necessary to trace over them with a fine brush charged with ink.

The short horizontal lines at the top and bottom of each figure, termed serifs, as well as the two circles that enclose the minute divisions, can be drawn with a sharpened point of the screw-bar compass.

=620.= _Second Method._ Lay on the dial to be treated, or on another of the same dimensions that has the hours well marked, a piece of tracing paper, so that neither it nor the dial can be displaced, and, using India ink and a fine drawing pen, accurately trace the hour figures and the minute divisions. When the ink is dry, invert the paper and trace the figures, etc., thus obtained on the other side of the paper, this time using a pencil instead of ink. Laying the paper on the dial so that neither can slip, pass with a rounded point of some soft metal over all the figures and divisions. Now remove the paper without permitting it to rub against the dial. If the pencil has been selected of a suitable degree of hardness, and the operation skilfully conducted, the marks showing the hours and minutes will be clearly visible, although faint, and, holding the glass to the eye, the several marks must be traced over with a fine brush or pencil. If this operation is performed carefully, the dial will present a very good appearance.

=621.= _Third Method._ Place the dial within a kind of large barrel that has at its center a thick pivot projecting. The three rules, D, F, J, Fig. 271, can be fitted on to this by their central holes so as to rotate on it. Being supported by the rim of the barrel, they will pass very near to the surface of the dial without rubbing against it. From an inspection of the figures it will be evident that D is used for forming the bars of an X, F for those of a V, and J for that of an I. Of course the serifs at either end of a numeral are made with the compass.

It is unnecessary to observe that if the edge of the rim be graduated, and the rules terminated by any convenient arrangement for arresting their motion at the graduations, the hours can be traced on a dial from which all marks have been erased. It then only remains to paint them in with ink.

=622.= =Inks for Painting the Hours.= Work up some clean lampblack in oil of spike lavender. Then add a small quantity of spirit varnish, and thoroughly mix the whole. This is applied with a fine brush, and the success of the operation depends very much on the selection of this latter.

=623.= _Another Recipe._ Mix together ivory black, pure wax, and turpentine; the more the turpentine is in excess, the more will the ink be colored. It is best adapted for filling in the figures engraved in dials, and a gentle heat should be applied to impart a smooth surface. Any irregularities in the painting may be erased by the aid of oil of spike lavender and soft bread.

HANDS.

=624.= =To Set a Watch-Hand in Position.= The most delicate part of this operation is the enlarging of the center hole of a minute hand and the closing of the hour hand socket when necessary.

Set the hand in cement on a brass plate that has a hole passing through at the point corresponding to the socket. The hole must then be enlarged with a semi-cylindrical drill to a diameter such that it will only be necessary to gently pass the broach through afterwards. The drill must not be worked too rapidly, and the plate may require to be immersed occasionally in water, so as to avoid heating the cement and thus loosening the hand.

When the hole in a watch-hand is too large, it may generally be sufficiently reduced by means of the staking tool.

=625.= =To Redden Watch-Hands.= Make into a paste (while holding over a lamp) a mixture of two parts carmine, two parts chloride of silver, and one part Japan varnish. Having spread some of this over the hands, lay them face upwards on a sheet of copper, applying heat until the desired tint is produced.

GLASSES.

=626.= =To Drill Glass.= A hole can be rapidly made in a piece of glass by using a steel spindle ground at the extremity to a point with three or four faces, and hardened in mercury. This spindle may be chucked in the lathe, or rotated between the finger and thumb, the point being moistened from time to time with turpentine or the mixture mentioned in article =594=. The glass operated upon should be held against the blade with the thumb or a pad immediately behind it, and should receive a gentle rocking motion so as to prevent the drill from choking in the hole formed; and as soon as the point appears on the other side, the drilling should be re-commenced from that side. It is a good precaution to mark the point at which the hole is required with a diamond or the steel point before commencing, and the pressure applied while drilling must be but slight.