French box locks manufactured during the eighteenth and nineteenth century are generally very simple mechanically speaking; many rely on, if not just one, only a few internal levers. The mechanism initially locks with one full anti-clockwise turn of the key but, unlike British locks, can then turn a further 360 degrees to essentially ‘double lock’ itself. The design of the internal lock bolt catered for this double throw action by having an elongated bolt arm. The reason for this double locking action is somewhat of an enigma as it doesn’t seem to enhance the overall security of the lock; one is left to speculate that it may serve to complicate and lengthen the work of the illegal lock picker.
The addition of a ‘curtain’ (a revolving metal keyhole sheath that prevents multiple lock picking tools gaining access to the levers) and unusually shaped drill pins help make these locks extremely hard to open without their characteristic keys, adding certain complication for any lock picker or locksmith with the unenviable task of key duplication. Drill pins in the shape of a heart, triangle, star, (playing card) spade, and cloverleaf have been known to be fitted to these French locks.
Made significant by its usage on the magnificent 1787 and 1791 French ’Nécessaire de Voyage’ boxes commissioned by Marie Antoinette, the cloverleaf shaped drill pin is believed to symbolise the Christian holy trinity.
French lock fittings are externally recognisable by their cylindrical links to the top link plate and circular entry points to the main lock housing. These attributes, though subtle, weren’t found on British boxes which instead had cuboid links to the top link plate and rectangular entry points to the main lock housing.
It wasn’t uncommon for some French boxes to be fitted with English Bramah patent or Chubb locks, but their inclusion necessitated the customisation of the link plates and lock entry points accordingly.