The clock dial is built in two parts and mounted on pillars, locked conventionally with taper pins.
In an unusual configuration, the clock face indicates seconds, minutes, hours and date.
The escapement wheel has 120 teeth, and the second hand arbor rotates once every four minutes. The window revealing the second transitions is a 90 degree quadrant, and the second finger arbor carries four fingers with only one showing at a time.
The minute finger arbor rotates once every two hours and shows two opposed fingers on a dial with two sets of 60 minute divisions.
The hours are indicated in a window, revealing four hours. Date is shown centrally in a small window.
The main dial is supported by pillars riveted to the rear of the face.
It might appear presumptive to tackle the engraving so early in the build, but I felt it prudent to do so as hand engraving can easily go wrong. It is better to engrave the dial satisfactorily before finishing complicated dial plates.
The engraving on the original clock is clearly of a high standard and no doubt produced by a premier engraver in the city of London. The face has undoubtedly been re-silvered on a few occasions and the engraving is therefore slightly worn, resulting in a lightening of the finer lines. I attempted to simulate the strength of the original engraving before black filling.
The art of engraving requires both confidence and spontaneity. When reproducing an eighteenth-century engraver’s work, one needs to understand his working method. For instance, how the engraver combined all the stroke sections of script lettering, since a letter is never executed in one continuous motion.
I practice a signature by drawing the letters four or five times larger than the original in order to familiarise myself with the engraver’s style. By the strength of the curve, I can sometimes tell whether an engraver was right or left-handed.
Script lettering needs to be optically centred as opposed to dimensionally centred. Capital letters are often flamboyant, decorated with light scrolls, which often upsets dimensional centring. The light tail scroll at the end of Harrison’s name was almost certainly added to improve an optical centre balance – a trick frequently used by engravers, myself included.
The art of hand engraving is one of the most challenging of horological skills to acquire. In my case, a lifetime of drawing has proved to be beneficial.