Lubricant Chemistry and Viscosity Classes

Historically, watch and clock lubrication relied on natural oils, notably purified sperm whale oil prized for its stability, and various vegetable and animal oils of less consistent quality; these were prone to oxidation, gumming and drying out at different rates depending on storage and use, which is part of why old, un-serviced movements are reliably found with degraded lubricant regardless of how carefully they were made.

Modern watch lubrication uses synthetic oils and greases engineered for specific properties: oxidation resistance, stable viscosity across a temperature range, and controlled spreading behaviour (oils are formulated to resist migrating away from a jewel or pivot, since migration, not just degradation, causes many rate problems in serviced watches). Major manufacturers each produce graded ranges distinguishing light, high-speed oils from heavier, high-load formulations, and specialised greases for the barrel and keyless works.

Viscosity class is matched to the mechanical demands of each location: escapement and balance-pivot lubrication needs a very light, low-viscosity oil since the balance must swing with minimal resistance and any drag directly reduces amplitude, whereas the mainspring barrel wall and arbor need a heavier grease that resists being flung off by centrifugal force and squeezed out under the mainspring's considerable coiled pressure. Keyless and motion-work parts, meanwhile, typically use a general-purpose grease chosen more for its resistance to drying and its adhesion than for minimising friction, since these parts are not part of the timekeeping-critical chain.

Using the wrong viscosity class at a given point is a subtle fault: too light an oil at a high-load point migrates and dries out quickly, giving good performance briefly followed by rapid failure; too heavy an oil at an escapement contact adds drag that lowers amplitude and can make the watch run slow or stop under low power, particularly in the 'lying-down' positions where gravity assists less. Correct lubricant selection by point is therefore inseparable from correct grade selection, and the companion lesson on oil selection by point develops the practical mapping of oil type to specific bearing location.

This lesson explains why lubricant chemistry matters and how professional oil ranges are structured; applying specific oils to a real movement is a bench skill requiring training, the correct oils (which are specialist and not generally sold in small enough or labelled-appropriately quantities to laypeople), and an accurate understanding of the specific calibre's original specification.