- Museum number
Watch housed in a gold coin.
Bar movement with keyless winding and hand set.
Club-tooth lever escapement; split compensation balance; keyless; very thin.
Movement with 19 jewels.
Case made from two gold five-pound coins, dated 1911.
With original leather covered wooden box.
- Production date
- 1911 (coin;case)
Diameter: 36.10 millimetres
Height: 16.20 millimetres (box)
Length: 69.50 millimetres (box)
Width: 53.50 millimetres (box)
- Curator's comments
Text from 'Watches', by David Thompson, London, 2008, p. 136-137.
The making of extremely thin watches was developed in Switzerland during the 1830s; for a fine example se registration no. 1958,1201.1283. Here the system is taken a step further with the watch being incorporated into the body of a gold coin. In order to achieve this, two coins would have been used. The first coin is turned away to produce a hollow centre to house the watch. The second gives up its outer face to provide the flip-open cover. The precision with which the work has been carried out is evident in the fact that no join can be seen between the flip-open cover and the body of the case which holds the movement and dial. A minuscule push button, hidden in the milled edge of the coin, opens the case.
The origin of the idea is obscure but certainly the Swiss maker Philippe-Samuel Meylan was one of the first to do it, and an example made by F.A. Meylan using a twenty-franc gold coin, dated 1826, can be found in the Neuchâtel Museum. The skill required to make such a watch should not be underestimated and it is a testament to the art of the watchmaker that such precision in manufacture could be achieved.
The coin used in this example is a £5 gold piece minted in 1911. On the obverse, beneath the portrait bust of King George V, are the initials 'BM' for Sir Edgar Bertram MacKennal, RA (1863-1931). This celebrated Australian-born sculptor and artist was commissioned in 1910 to design the Coronation Medal for King George V, and this was followed by designs for new coinage. The reverse of the coin depicts St George and the dragon with 'BP' beneath. These are the initials of Benedetto Pistrucci (1783-1855), a renowned engraver and die-cutter who was born in Italy but came to England where he worked at the Royal Mint from 1815 onwards. This St George, which he designed and produced in 1817, is perhaps his most famous work.
The watch housed in the coin is unsigned, but it is a well-made, typically Swiss example of the period. The movement is a standard, high-quality 19-jewel calibre with club-tooth lever escapement. The fine, matt-finish, buff-coloured dial is identical to those found in other small watches of the period and the moon-pattern pierced blued-steel hands are typical. The difference here is that the winding button is set at neither 12 o'clock nor 3 o'clock, but is off-set at about 2 o'clock to allow it to fit inside the case. The watch then swings out on a hinge to facilitate winding and setting. Although unsigned, the movement calibre is similar to those made in Schaffhausen by the International Watch Company.
Comment from Richard Good, Catalogue of Watches in the British Museum. Vol. V (Unpublished manuscript)
Switzerland, c. 1960
Gold coin watch with a club tooth lever escapement
Box: A red box with a hinged lid embossed in gold "Coin Watch".
Case: A gold £5 piece of 1911(2) hollowed out so as to act like a hunter case. The slide bearing the monarchs head has a secret hinge and a press piece allows it to spring open. The inner case is also hinged so that it can be lifted out for the winding and handsetting.
Dial and Hands: Metal canister dial with Arabic numerals. Blued-steel moon hands.
Ebauche Marks: 28298
Frame: Bar movement with a hanging barrel. The pallet bridge in steel.
Barrel and Mainspring: A recessed cover to the going barrel
Barrel: I diameter 8.00 mm., height 0.6 mm.
Mainspring: height 0.55 mm.,(3) thickness 0.10 mm
Arbor: diameter 2.8 mm., snailed
Train: Wheels gilded with 5 crossings the steel escape wheel with 4.
Jewelled: from the centre onwards except that there is no centre jewel in the front plate. Endstones of ruby to the balance and escape wheel.
Escapement: Club tooth lever, straight line layout, short lever, double roller, impulse pin triangular in section and set directly into the balance arm. Pallet stones exposed, the acting faces flat. A steel escape wheel, recessed.
A mixed escapement
No. of teeth embraced 3½
Balance: Split bimetallic balance with compensations screws of brass4. Balance diameter 7.35 mm., thickness 0.36 mm. Blued steel flat spiral spring with 14 turns.
Means of Regulation: Index on the balance cock registering against a divided scale with engraved 'ADVANCE RETARD'.
Train Counts and Beat Rate:
Great Wheel (barrel) 76
Centre wheel 64 pinion 10
Third wheel 60 pinion 8
Fourth wheel 60 pinion 8
Escape wheel 15 pinion 6
Beat rate: 18,000
Motion work: cannon pinion 10
Minute wheel 30 minute pinion 8
hour wheel 32
Winding System: Conventional positive stem set keyless work.
Dimensions: Box 53.5 mm. across, 70 mm. long, 16 mm. in depth.
Coin diameter 36.15 mm., thickness 3.7 mm.
Movement diameter 20.2 mm., height 2.3 mm.
Provenance: Purchased in 1969.
(1) The movements for these watches were probably made by Piguet.
(2)Two coins are required. If only one coin is used the front cover cannot be separated from the coin so as leave the full thickness on the coin edge.
(3) This mainspring, height 0.55 mm., must be one of the least in height made.
The screws in this balance must be amongst the smallest ever to be made with a thread diameter of only 0.2 mm.
These flat movements are the most difficult of all horological objects to make. All the wheels must be absolutely flat and their relative heights very carefully controlled. The dial plate becomes so flimsy where it is cut to clear the keyless work that special precautions must be taken. In this watch around this area two extra screws are used to connect the dial plate to the barrel bridge. The keyless work is excessively difficult to make, the sliding pinion is only 1.18 mm. in diameter and has only 7 teeth at either end. Though its middle is a square of 0.45. mm diameter. The escape wheel is 0.22 mm. thick, the thickness of an average piece of card.
- On display (G39/dc14/no72)
- Latest: 2 (2016)
- Acquisition date
- Britain, Europe and Prehistory
- Registration number