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Radium
Radioactive luminous material first used on the hands of watches around 1913. This material was subsequently replaced by Tritium around 1950.
Reference Number
The case or model number of a watch, usually engraved between the lugs, and/or inside/outside the case back.
Reflection
The bouncing back of light when it strikes an external or internal facet on a polished diamond.
Refraction
The change in direction of a ray of light as it passes obliquely from a medium of one optical density to a medium of a different optical density, as from air into water or from air into a gemstone. This means that the light bends as it enters a diamond because the light travels through air and the diamond at different speeds.
Refractive Index
A process using a refractometer to measure the speed and angle of light entering a gemstone. Very important for gem identification.
Registers
Term used to describe the subsidiary ‘extra-function’ dials positioned on the face of a chronograph watch.
Rhinestone
A facetted piece of glass or quartz that has a foil backing in order to imitate a diamond.
Rhodium Plating
Rhodium is metal that is part of the platinum family. White gold is commonly rhodium plated in order to give it a very white finished color because white gold is not purely white but instead has a yellowish tint It is also used on silver to prevent it from oxidizing.
Rolesium
A Rolex term used to describe the case metal mixture of stainless steel and platinum, trade-marked on May 21, 1932. This configuration is currently seen on the Rolex Yacht-Master.
Rollesor
A Rolex term used to describe the case metal mixture of stainless steel and gold, trademarked on April 1, 1933.
Roman-Arabic Dial
See also California Dial.
Rose Cut
An early style of cutting that is thought to have originated in India and to have been brought to Europe by the Venetians. In its most usual form, it has a flat, unfaceted base and a somewhat dome-shaped top that is covered with a varied number of triangular facets and terminates in a point. The rose cut diamonds are very seldom used today but may be seen in antique pieces.
Rotating Bezel
Often used on sports watches like divers’ or aviator models, it is used to perform an additional function, such as checking decompression times, or telling the time in different time-zones – See also Bi-Directional Rotating Bezel and Uni-Directional Rotating Bezel.
Rotor
The oscillating weight used in an automatic movement.
Rough
In gemology, this refers to the raw, natural state in which gems are found, before they are cut.
Rough Girdle
When a diamond outer shape is formed in the cutting process it is done by grinding one diamond against another. This should leave the surface of the girdle with a smooth and waxy luster. If a diamond is rounded up too quickly in the fashioning process it will leave it grainy or pitted. It may also be accompanied by numerous hair like fractures extending into the stone, which is called a bearded or fuzzy girdle.
Round Brilliant Cut
This is the most common cut for a diamond. The standard round brilliant “full cut” diamond consists of a total of 58 facets: 1 table, 8 bezel facets, 8 star facets and 16 upper-girdle facets on the crown; and 8 pavilion facets, 16 lower-girdle facets, and usually a culet on the pavilion.
Rounding Up or Girdling
The step in the fashioning process of a diamond in which the stone is given its overall shape. The stone is held in a lathe, or cutting machine, and another diamond, called a sharp, which is affixed to the end of a long dop that is supported by the hands and under an armpit, is brought to bear against the stone behind shaped. An older method consisted merely of rubbing two diamonds together until the desired shape was obtained.
Rubellite
Used to refer to the red variety of tourmaline, including the color range from pink to red. More of a marketing than a gemological term; these days gemologists tend to use simply “red tourmaline.”
Ruby
See Jewel.
Rutiles
Needle-like inclusions (or foreign matter) within stones. These can produce some gem phenomena as an asterism (star) or cat’s eye (chatoyancy.)
S
A grade in GIA’s Color Grading System…. at the beginning of the “Light Yellow” category.
Sapphire Crystal
First introduced in 1970, on the Rolex Quartz, these synthetic crystals are now used in most watches, due to the fact that they are highly scratch resistant.
Saturation
Saturation is one of three characteristics used to describe the appearance of color. Saturation (also known as intensity) refers to the brightness or vividness of a color. See also hue and tone.
Sawable
These are rough diamonds that can be divided by sawing.
Sawyer
A person who has the job of sawing diamonds.
Scaife
The horizontal cutting wheel on which a diamond is polished… also spelled scaive or scaif.
Scintillation
The flashes of light reflected off of the facets of a diamond when the diamond or the eye of the viewer moves. This is the bling factor! The number, the size, and the quality of the polish of the facets are all factors in the scintillation.
Scratch
A fine white line, curved or straight on the surface of a diamond. A scratch would be considered during the clarity grading process. A scratch can be polished away.
Self Winding
See also Automatic Winding.