D

Dial, Break-Arch:
( Pic )     An early form of arch dial: the top of the main, square dial is surmounted by a semicircular arch, slightly smaller in diameter than the width of the dial, leaving a small step or break at the base of the arch.

Dial, Enamelled :
( Pic )     White enamelled dials were first introduced in England in the 1740s for watches, and for bracket clocks later in the 18th century. Enamel dials were more legible than the engraved and silvered type, and were made by melting a vitreous enamel on a copper base. As the muffles used in the process were only suitable for small objects, it was difficult to produce the larger dials required for longcase clocks, which are therefore extremely rare. Another drawback was that the enamel surface was brittle and tended to crack or flake if subjected to even a small amount of shock or torsion, especially where the dial feet were riveted into position.

Dial, Equation :
A rare form of auxiliary dial which indicates the difference between solar and mean or average time. Most early longcase clocks were sold together with a sundial which was an essential adjunct to the clock in order to set it to time. However, a simple conversion from solar time to mean time had to be first worked out. Solar time, according to the season of the year, could be almost 16 1/2 minutes fast or slow of mean time. This difference was shown automatically by the equation dial, though a cheaper substitute was available in the form of a printed equation table, which could be stuck on the inside of the door of the clock for easy reference.

Dial, False Plate :
( Pic )     Towards the end of the 18th century the majority of longcase clock dials and movements were prefabricated in a number of regional centers, and painted iron dials became popular. The iron dial was supplied with a false plate already attached, leaving the 'maker' to drill holes in the front movement plate in a convenient position in relation to the working parts. The dial feet were fitted in the false plate instead of in the previously painted dial - a method which would clearly have been impossible without damaging it. Cast-iron false plates often carry the name of the manufacturer, most of them being made in Birmingham. False plates are mostly found on eight-day, not 30-hour clocks.

Dial, Glass :
( Pic )     Glass dials are simply clock glasses on which the hour and minute numerals are marked instead of on a conventional dial. Such dials make it possible to see the movement of the clock in the same manner as in a skeleton clock. Although not common, glass dials are found on some early Connecticut shelf clocks, on a type of keyless rack clock made in the 1920s, and on a famous one-wheel clock invented by Pierre Le Roy in the 18th century. Another form of glass dial is used in a type of 'mystery' clock in which the hands are marked on revolving glass discs, driven from their edges, the clock thus appearing to have no movement.

Dial, Lunar :
( Pic ) ( Lunar Month )   A subsidiary dial, usually situated in the arch but sometimes found as a segmental aperture in the main part of the dial, or as a circular aperture known as a 'halfpenny moon', or as the 'Halifax moon'. The complete lunar cycle takes almost 29 1/2 days, and the purpose of the lunar dial was to record automatically the lunar phases. Although a lunar dial has often been regarded simply as an interesting addition to the dial, it was of great practical use in the days before street lighting.

Dial, Painted :
( Pic )     Painted dials were introduced shortly after the middle of the 18th century. The design of regional brass clock dials had become so cluttered with decoration, auxiliary dials and sometimes as many as four separate hands from the dial center (hour, minute, center second sweep and calendar hand), that it was often difficult to tell the time at a distance. The solution was a white enamelled or painted dial. Large enamelled dials were difficult to manufacture, so the painted dial was adopted. It proved eminently functional, as well as being cheaper and easier to produce than the engraved brass dial with its separate chapter ring and spandrels. Early painted dials were designed in a restrained and elegant manner, in keeping with the other decorative arts of the Adam period. However, popular demand soon called for the production of more colorful dials with painted scenes in the corners and arch.

Dial, Regulator :
( Pic )     In a regulator for astronomical purposes the dial is usually arranged with separate circles for hours, minutes and seconds, the outer circle being for minutes and large subsidiary dials below and above the center indicating hours and seconds. In some such regulators the motion work is dispensed with to reduce friction, necessitating separate setting for hour and minute hands. In England the seconds dial is usually above the center and the hour dial below. In the United States, where E. Howard & Co. produced most of the clocks of this type, the location is often reversed and the seconds indicated at the six o'clock position. A special light form of Graham escapement, with the anchor moving in the opposite direction to the pendulum, makes this feasible. Watchmakers' regulators were also made with this type of dial.

Dial, Skeleton :
A dial cut away to reveal the action of the clock movement behind. Always used in skeleton clocks, it is sometimes also found in high-quality regulators. Turret-clock dials made of cast iron with glazed apertures for back lighting are a form of skeleton dial.

Dial, Strike or silent :
( Pic )     Usually found in the arch of bracket clocks but also in some longcase clocks. Bracket clocks with verge movements were portable, and the owner, on retiring to bed, could take his bracket clock with him and turn the hand of the strike/silent dial to 'silent' so that he would not be disturbed by the clock striking while he was asleep. The strike/silent mechanism was only made possible by the introduction of rack striking at the end of the 17th century. Longcase clocks were not, of course, portable but silencing the striking mechanism at night is sometimes no less desirable.

Dial, Thirteen-piece :
( Pic )     A form of enamel dial fashionable in France c. 1750, composed of twelve wedge-shaped car-touches bearing the hour numerals, fitting closely around a circular domed centerpiece painted with the maker's name. Enamelled hour plaques, set in a gilt-bronze frame and having a gilt-bronze centerpiece, had been popular since the late 17th century. The enamelling was done in specialist workshops, the white ground being produced by an enamel with pewter oxide, the black, or more rarely blue, numbers being added as a final firing. About 1715 a white enamelled center to the dial became fashionable, but the bronze frame persisted, and it was not until 1740 that reference is made to a clock with a dial entirely of enamel. The 13-piece construction was necessary because of the technical difficulties in producing large enamelled dials, difficulties which were not overcome until later in the century.

Dial, Tidal :
( Pic )     A fine example of the clockmaker's ingenuity. Two sets of Roman numerals, from one to twelve, were engraved, usually in the dial arch alongside the 29 1/2 days of the moon's phase. By adjusting an indicator it was possible to forecast the approximate time of high tide at any given port. This was of particular value to mariners when ship departures depended on the tide. John Flamsteed, the first Astronomer Royal, is said to have drawn up tidal tables for use in the Port of London, the calculations being worked out in conjunction with the changes in the moon's phases.

Dial, Universal-time :
( Pic )     For some time clockmakers have attempted to show the comparative time in different parts of the world; this became really important after the invention of the electric telegraph. A clock by Thomas Lister of Halifax, Yorkshire, c. 1780, has a special dial from which the time in 24 places in the world can be calculated with reference to the main dial. Some chapter rings on 18th-century longcase clocks have the names of various foreign towns engraved on their outer edge: when the hour hand of the clock is opposite these names it is noon in the respective places. In the 19th-century large universal-time clocks, or world-time clocks as they are sometimes known, were installed in the offices of commercial organizations with worldwide interestes. These had multiple dials to show time in the principal cities of the world, the dials being set in phase with the main movement of the clock.

Dial, Up and Down :
A subsidiary dial, usually in the twelve o'clock position on a marine chronometer or precision pocket watch, which indicates the degree to which the mainspring is wound at the time of observation. It was usually fitted when failure to wind the timekeeper would have serious consequences, as on a chronometer used for longitude determination. On a fusee timepiece it consists of a pinion placed on the fusee arbor which moves a high-numbered wheel with an arbor carrying a hand, so arranged that a full run of the spring will carry the hand somewhat less than 360º. On going-barrel pieces it is much more complicated and sometimes employs planetary gearing.

Dial, Velvet :
Although rarely used on English clocks, velvet-covered dials with separately attached engraved and silvered chapter rings are not infrequently found in certain European bracket clocks produced towards the end of the 17th century. These clocks had somewhat plain, architectural or rectangular cases and were known as religieuse clocks in France and Haagse klokje in Holland. Also mounted on the deep blue or wine-colored velvet, just below the chapter ring, was a cartouche bearing the maker's name. A more elaborate bas-relief mount is also found in which a gilded or silvered figure of Father Time with his scythe supports the cartouche.

Dial, Wandering Hour :
Normally associated with certain watches of the late 17th and early 18th centuries, though a few such dials were made for both longcase and bracket clocks. These were night clocks, the figures occurring as slits behind which the light from a lamp shines through to show the time. In this type of dial the hour appears in a disc which advances from left to right across a segmental slot marked along the edge in minutes and quarters. As one hour completes its journey along the slot the next hour appears on the left, marking the divisions of the following hour. There were two basic methods by which this action was achieved. In one, the hour discs were formed into a twelve-piece chain carried around a ten-sided wheel, bringing the correctly numbered disc into place at each succeeding hour. The other system employed a large revolving disc with two small revolving discs mounted on it opposite each other, one bearing the odd numbers I to XI and the other the even ones II to XII. Each smaller disc rotated one figure at each half-revolution of the main disc, bringing the respective hours into view as they moved along the aperture in the dial.

Dial, Wooden :
Wood as a material for turret-clock dials has been universally used, but for domestic clocks the wooden dial seems to have been limited to clocks made in the Black Forest, other European peasant communities and North America, up to the early 19th century. The Black Forest dials were mostly made of fir, which tends to split after a time. The dials were made by cutting boards to shape and gluing a second layer to the first in the shape of a circle, to form the figured part of the dial. The whole was then turned on a primitive lathe so that the figure portion formed a slightly convex shape, its surface gently merging with the base of the dial. The pores of the wood were filled with size and lime-water and the figures and decoration painted on, after which the whole was given one or more coats of varnish. Dials were packed in paper and were not fixed to movements until the whole consignment of movements, dials, chains, bells, etc. had reached its destination. The dials were made and painted by different craftsmen and fitted to movements by many makers in the same area.

Dial Clock :
( Pic )     During the latter half of the 18th century the English dial clock appeared, a descendant of the so-called 'Act of Parliament' or 'tavern' clock. Originally timekeepers only, consisting of a large circular dial about twelve inches in diameter with a spring-driven fusee movement, the early examples had a verge escapement and often a convex silvered dial. The dial was secured to a circular wooden surround, the rear of which had two wooden strips attached to locate its position on a rectangular wooden box, then pegged into position to hold the clock. A hook on the box allowed the clock to be hung on a wall. Later, dial clocks became more ornate and often incorporated striking trains and sometimes an alarm, the anchor escapement being universally used, with a door in the box to allow the pendulum to be seen or started. Modern dial clocks may have balance-controlled escapements, synchronous electric movements or, increasingly, battery electric movements, including quartz-crystal types.

Dial Feet :
Clock dials are attached to the front plate of the movement by means of short cylindrical pillars, which are riveted to the dial so that they cannot be seen from the front. They are usually sited so that the riveted ends are concealed beneath the chapter ring. The ends of these dial feet pass through holes in the front plate of the movement and are secured with tapered steel pins. There are usually four dial feet on an English longcase dial but country-made 30-hour clocks are often found to have only three.

Diamantine :
A white powder prepared from boron, processed to obtain the utmost purity. It is normally obtainable in three grades and used with a little oil for finishing and polishing steel. The coarsest grade, No. 1, is for grinding and smoothing, while grade No. 2 is commonly used to obtain the final polished finish. Grade No. 3 is exceedingly fine and little used by clockmakers.

Die :
( Pic )     One kind of die is a tool used for cutting a thread on a rod. It usually takes the form of a disc of tool steel, with a center hole and two or more radially disposed holes which break into the central hole to form cutting edges. The central hole is first tapped with the required screw thread. The outer edge of the disc has flats or shallow holes which allow it to be gripped in a die holder or die stock when in use. The finished die is hardened and tempered, and some dies have a slit from one edge to the center hole to enable this cutting hole to be opened or closed slightly when fixed into the stock. Split dies are made in two halves which are put together in the screw stock; they normally have one size of thread only, but are sometimes made with a number of differently sized holes in the split. A die nut is similar to an ordinary die but of hexagonal or square outer shape for cleaning up threads and useful for threads which cannot be reached with dies held in stocks. Another, entirely different tool called a die is a shaped metal block used to produce a form or shape by metal stamping or pressing; these are called 'metal-forming' or 'punching' dies. Die casting is a process in which molten metal is forced under pressure into a die or mould to produce a casting.

Digital Clock :
( Pic )     Any clock which indicates the time by a display of figures rather than by a dial.

Dividers :
( Pic )     Dividers, or measuring compasses, differ little from compasses exept that they are spring-hinged and are adjusted by a knurled nut and screw for fine measurement. They are used for taking comparative measurements, as a drawing instrument, or for scribing out a clock plate.

Dividing :
This term refers to dividing the length, diameter or circumference of circles as required, by means of dividers or dividing plate, or by other means. Clockmakers use dividing plates to produce wheels, pinions, count wheels or locking plates, and other clock parts such as dials.

Dividing Plate :
( Pic )     A flat circular plate fitted to a wheel- or pinion-cutting machine, or to a lathe spindle or dividing accessory for a lathe or other machine. On the plate a number of concentric circles are marked, each divided into a different number of equal divisions. Work held on the arbor of the dividing plate can therefore be rotated and divided according to the number of divisions, using a detent located on a selected circle. Alternatively the dividing plate may have teeth on its edge, driven forward by a worm or endless screw, and advanced to the required position by a previously calculated number of rotations of the worm. A useful method of marking out a dividing plate, used by Henry Hindley of York early in the 18th century, is to cut a series of small, equally spaced holes in a long strip of metal, equal in number to the largest number of divisions required on the plate, plus an extra one. The strip is bent to form a complete loop and the two end holes joined by a rivet or peg. A disc of wood is then turned on the lathe until the loop fits tightly around its circumference, which is thus divided into the required number of equal divisions. These divisions can be transferred to a circle on a blank dividing plate and the same strip of metal reduced in stages to produce decreasing numbers of divisions on smaller circles on the dividing plate by the same basic method. The position of the first division of each circle on the dividing plate is usually placed on a radial line, with the numbers of divisions clearly marked for each circle.

Divination Boards, Chinese :
Divination boards were fairly common in China. They consisted of a round disc, of various diameters, usually of wood either lacquered or varnished. In the center was a magnetic compass, and around it, covering the entire surface, was a circular azimuth chart. It had the characters for the cardinal points of the compass, the Twelve Terrestrial Branches, the Ten Celestial Stems, and other calendrical characters at various intersections of the radial and concentric lines on the chart. On the back of the disc were painted other similar characters in a rectangular chart. The charts were used to measure the degrees of azimuth of certain natural phenomena that were thought to influence the course of events. In this way auspicious and inauspicious days were established, and the proper rituals were observed to celebrate fortuitous occurrences, to ward off calamities, or to appease vengeful spirits, whichever seemed to be necessary in the astrological circumstances prevailing at the time. In a modified form, these charts appear around the compasses of Chinese sundials. Other, earlier forms of divination boards appeared on the dial surface of ancient sundials and on TLV mirrors (mirrors bearing marks resembling these letters) of the Han period (206 BC - AD 220). The specific use of the earlier boards is even less clear than that of the later models.

Dolphin Fret :
( Pic ) ( Pic )   The figures of a grotesquely shaped, scaly fish with a large head and curved tail standing high above it, was a favorite motif in baroque decoration. Legs of tables and arms of chairs were frequently carved in this form, known as a dolphin and resembling the ocean fish, not the mammal, of that name. Dolphin frets may be seen masking the bell lantern clocks, and more often as supports on either side of the boss in arch-dial clocks. Like spandrel mounts, they are cast, chase and gilded, and attached to the dial with small screws.

Drawbench :
( Pic )     A long, strongly built bench used for drawing lengths of wire to a desired section. One end of the bench is fitted with a large capstan or wheel, and the other has supports to hold the drawplate. The wire to be drawn is threaded through the drawplate and clasped in the jaws of special draw pliers which are hooked to a strong leather belt. The other end of the belt is wrapped around the arbor of the wheel. As the wheel is turned the belt tightens and pulls the wire slowly, with great force, through the drawplate.

Drawplate :
( Pic )     A hardened steel plate in which a number of graduated, tapering, round or suitably shaped holes have been formed to enable wire to be drawn successively through diminishing sizes of holes, to be reduced in diameter. Plates may be obtained for drawing round, square, half-round, triangular or other sections of wire. When a wire of a certain section is needed, a wire of slightly larger diameter is prepared with a long taper at one end which is passed through the larger side of the largest hole in the plate. The wire is then steadily pulled through the hole by means of the drawbench, which squeezes the wire into the shape and reduces its size. Repeated drawings through diminishing sizes of holes bring the wire to the required size and section, but after a number of drawings it should be annealed, otherwise it will become too hard and may break. Pinion wire for making small clock pinions is produced by drawing wire through plates with holes gradually shaped to the pinion section.

Drill, Archimedean :
( Pic )     A hand tool which gives reciprocating motion to a drill. It consists of a rod with a spiral 'quick' thread, having a handle pivoted at one end and a drill holder or chuck at the other. A sliding nut on the threaded rod imparts motion to the drill. Some drills of this type have the nut formed in the base of the handle, the rod passing into the handle as pressure is applied and returning by means of a spring when pressure is released, thus giving reciprocating drill action. Another type of drill often referred to as archimedean is the drill with cords and inertia wheel. This is also called a 'bob' drill or 'upright' drill, the weighted bob causing the cords to wrap around the stock on the overrun, motion being imparted as the handle is pressed down. This type is normally used only by jewellers and casemakers.

Drill Arbor :
( Pic )     A spear-shaped tool or flat drill having cutting edges on the flattened end, a male center at the other end and a pulley, or ferrule, on its elongated shank. It is rotated for drilling by the use of a drill bow, which produces reciprocating motion. In use the drill arbor is supported at the cutting end by the drill point and at the other in a center hole of a breast plate, or in a hole in the end of a vice jaw or vice block. This type of drill, depending on the exact shape of the cutting edges, when used with plenty of oil will penetrate hard brass or even tempered steel. The name is also given to pintongs which are intended to hold a drill and be rotated in a large chuck or collet.

Drill Bow :
( Pic )     The bow is used to impart reciprocating motion to work in the turns, to the spindle mandril of a lathe, to a drill or drill stock, or to an arbor, by coiling the line of the bow once around a pulley or ferrule. As the bow is moved to and from the work rotates in alternate directions. Bows are made of thin strips of whalebone or cane, drill bows usually being of flexible steel with a tensioning device at one end. Various sizes of bow are available and, according to the size and nature of the work, gut, horsehair or human hair is used for the line.

Drill Box :
( Pic )     A drill holder with a square box-shaped aperture at the end of a drill stock or drilling tool. A screw-nosed drill box has a nut on a tapered slotted nose box by which the nose is squeezed or closed to secure the drill. Drills for use in a drill box have a square shank.

Drilling :
There are drills for numerous different purposes. Two basic methods are employed when drilling: rotating the drill with the work stationary, or rotating the work with the drill stationary. When drilling holes in clock plates or other parts it is convenient to hold the work still on a drilling table, but when drilling down the axis of arbors or pinions greatest accuracy is achieved by rotating the work in a lathe. Drills are rotated by a bow, drill or wheel brace, archimedean drill or drilling machine, while work is rotated in a mandril or lathe for making a hole with the use of a boring tool.

Drill Stock :
( Pic )     A steel arbor fitted with a ferrule, a male center at one end and a drill holder at the other. Available in various sizes, it is rotated for drilling by a bow. Some drill stocks have a simple tapered box or screw-nose drill box or chuck; others have a plain round hole for the drill with a hole in the side of the stock and screw-set collar to clamp the drill in position. In use a drill stock is supported in a frame, or operated like a drill arbor.

Drop Dial Clock :
( Pic )     Similar to the dial clock but with the addition of a trunk below the dial, allowing a longer pendulum, for better timekeeping, and additional carved decoration. A glass panel is usually fitted to allow the pendulum bob to be seen; often these clocks also strike on a bell. The original drop dial clock is a typical English design dating from the mid 18th century, later produced in vast quantities in the United States, where they are known as 'school' or 'regulator' clocks. The quality of these is not to be compared with the English drop dial fitted with spring-driven fusee movements.

Drop Octagon Wall Clock :
( Pic )     The octagon wall clock with a lever movement and an 8in. dial with brass bezel became popular c. 1850 as a timepiece for travelling by sea or rail. The drop octagon, with pendulum movements, striking and silent, installed, is believed to have been introduced by Chauncey Jerome for the London Great Exhibition of 1851. The case design was a modified, abbreviated English Act of Parliament type. The usual dial size was 12in. The earliest models had a veneered octagon top with a projecting compartment at the base and a glass-panelled door revealing the pendulum. Frequently, carved pieces were mounted flanking the door and extending on each side of the base octagon section. This style of timepiece was available as an eight-day striker and was occasionally furnished with an alarm. It was the forerunner of what became known in North America as the 'schoolhouse' clock, manufactured in millions until c. 1930.

Drum Clock :
( Pic )     Table clocks of the 16th century can be divided roughly into two groups, tower clocks and drum clocks. On the former the dial was vertical and on the latter it was horizontal, occupying most of the top surface of the clock. Some drum clocks were small and plain, and this design eventually developed into the watch and, much later, the marine chronometer. Some drum clocks, however, were quite large, with richly decorated cases and even additional dials. In some instances the clock was arranged to stand on three feet. In the last quarter of the 19th century the shape came into vogue again but now standing upright, in the still-popular style of the alarm clock. A good selling point was that the clocks were portable and did not have to be set in beat like a pendulum clock. Millions of the type must have been manufactured before 1900. A finer version came from France, with the drum of sheet brass, the spring contained in a barrel, and the escapement mounted on a separate platform screwed to the movement. More rarely a tiny pendulum with tic-tac escapement was fitted.

Drum Clock, Chinese :
( Pic ) ( Pic )     Truly Chinese, such clocks are in the form of an oriental drum, designed to be supported vertically on a stand. The cases are pierced engraved chased brass cylinders of varying diameters, all about 3in. deep. The movements vary, but all are copies of European timepieces and similar in workmanship. Since the Chinese hour system closely matched the western diurnal system there was no need to adapt the mechanism in any major way. Chinese clocks have twelve fixed equal hours, with no way of altering either the dial or the rate of escapement for a system of varying hour lengths. Most have alarms, consisting of a brass setting disc, with six small knobs and a window, placed over another disc with the Twelve Terrestrial Branches, representing the twelve fixed hours, each marked with a Chinese character, closely associated with the twelve animals of Chinese folklore, engraved on it, fastened directly to the dial plate. Not many of these clocks were made and, although they can be found, they are not common.

Drum Table Clock, Japanese :
Adaptations of European table clocks, they were not modelled after an oriental drum on a stand nor displayed vertically, and are therefore called table clocks. Almost all such clocks are from a late period, after the 18th century, and feature revolving, adjustable chapter rings and a fixed hand. The engraved decoration tends to be of the common variety found on Japanese clocks. The cases are cylindrical brass drums with simple verge balance-wheel movements and horizontal dials.