Alloy

Combination of two or more pure molten metals. Generally, an alloy is given the name of the dominant metal.

Block

In a lever escapement, the dart is fixed to a block at the base of the fork.

Champlevé(e)

Describes a metal surface that has been hollowed using a graver to form cells that will be filled with enamel.

Decimal hour

A decree of October 5th, 1793, promulgated on November 24th of the same year, introduced the French Revolutionary (or Republican) calendar, based on the decimal system. It was declared to...

Ebauche

An unfinished movement sold as such. Until circa 1850, an ébauche comprised only the plate, bridges, fusee and barrel. It was known as a blanc and was finished at the...

Fracture

A break in a gemstone.

Gemmology

The study of precious stones.

Hematite

A natural iron oxide that is a metallic dark to silver-grey with a high sheen. Hematite can be used to make watch dials. It has a specific gravity of 4.95 to 5.16 and a hardness of 6.5 on the...

Impulse

In a lever escapement, the action of the escape-wheel tooth on the impulse-face of the pallet.

Jewels

The international term for the jewels (rubies) in a watch movement that are used as bearings for pivots to reduce friction. The movement of a quality watch has between 15 and 21 jewels.

Knot

A raised mineral inclusion in a diamond found at the surface.

Ligne

Also "ligne parisienne". An old unit of measurement in traditional watchmaking, prior to the metric system and directly inherited from the French pied (foot) under the Ancien Régime. One...

Micron

A metric unit of length equal to one thousandth of a millimetre or one millionth of a metre. The watch industry often expresses tolerances in microns.

Nephrite

A family of the jade group of ornamental gemstones. Nephrite is slightly softer that jadeite and is often veined.

Oscillating weight (Rotor)

In a self-winding movement, a heavy metal disc that turns freely in both directions to wind the mainspring.See rotor.

PVD

Physical vapour deposition, a technique for coating metal.See electroplating and plating.

Quartz

Silicon dioxide. Also called rock crystal. Quartz has the specific property of vibrating at a very high frequency (32 MHz) placed under electric current. Under certain conditions, it...

Refractometer

An instrument that measures the refractive index of a gemstone.

Subsidiary seconds

As opposed to centre or sweep seconds, a small subdial showing seconds, generally at 6 o'clock.

Universal hour

One twenty-fourth of the universal day which begins at midnight at the Prime Meridian at Greenwich. Following the 1884 International Meridian Conference in Washington, the Earth was divided...

Vermeil

Silver covered with a thin layer of gold.

Waterproof

Describes a watch which, in theory, will not let in water at a depth of up to 3 atm or 30 metres.See also ATM; water-resistant.

Year

A four-digit indication of the current year that changes automatically at midnight on December 31st.

Zinc

A metal applied by electrodeposition (electroplating) to protect iron and steel.