A gem that is cut round without facets into the shape of a smooth polished dome. It lacks the facets that are on most stones.
A watch with a mechanism that shows the date, or on the more complex watches, the month, day, moonphase, and even the year. Most calendar watches have to be adjusted manually at the end of the month, but the mechanism of a perpetual calendar watch adjusts itself automatically.
Caliber (or Calibre U.K.)
Refers to the size, style, or shape of a watch movement.
Many gemstones are sold in calibrated or standard sizes that will fit commercial jewelry settings. Standard sizes are calibrated in millimeters for a number of different gem shapes.
California Dial (Also Roman-Arabic)
Dial featuring a combination of Roman & Arabic numerals; Roman on the top half, with Arabic on the bottom. The term “California Dial” refers to a California-based company who became known for reproducing the dial over the years.
Fancy color diamonds with an intense yellow hue similar to that of a canary bird. The yellow may be very slightly greenish or slightly orangey.
An outdated diamond color term referring to diamonds with a yellowish body color. This term originally referred to the Cape of Good Hope, referring to South Africa. The body color of diamonds produced by the South African mines was distinctly more yellow than the average diamond body color of Brazilian diamonds. This term is almost never used anymore because it is very inaccurate.
A unit of weight for gems. A carat is one fifth of a gram (0.2g).
The measurement unit for the weight of gemstones. The origin of the word carat is from the seeds of the carob bean that were used to balance scales in ancient times. In the early 1900s the metric carat was standardized as one carat equaling 200 milligrams. When you buy a diamond the weight of a diamond is measured out to the hundredth of a carat (2 places to the right of the decimal point). It is expressed as “ct.” or “Ct.”, for example 1.23ct.
Carbon or Carbon Spots
This is a term used by some people in the jewelry industry to describe the appearance of certain diamond inclusions that appear black… typically a dark included crystal. Diamonds are 99.95% pure carbon; but 25 other different mineral inclusions or small crystals, have been found within diamond as well. These are not carbon spots, but rather small crystals that were trapped within the host diamond as it was forming in nature. Sometimes, they just happen to be dark in color. The most common mineral found within diamond is diamond.
An inclusion consisting of a large or deep opening in the diamond.
Center Seconds (or Centre Seconds U.K.)
Also called sweep seconds. Mounted on the center post of the watch for greater visibility and ease in reading.
The main stone in a piece of jewelry with multiple stones. This stone is usually the largest and most prominent.
Certificate or “Cert”
Another term for a Diamond Grading Report. A document produced by a disinterested 3rd party (typically a Gemological laboratory) that describes a diamond’s characteristics. This report should only list the characteristics of the diamond and not refer to any prices.
A title awarded by the American Gem Society to qualified members. To qualify, a person must study colored stones and their identification, along with diamond grading and appraising. Also they must prove proficiency with several written examinations and a diamond-grading examination.
A diamond that has a color similar to… you guessed it, champagne!
Diamonds set into a row where the diamonds are held into place by grooves cut into a strip of metal along the edge of the piece of jewelry. Used quite often for wedding and anniversary bands.
The city in southeastern Thailand famous as one of the world centers for gemstone processing and trading. Chanthaburi is also famous for its weekend gemstone market.
The cat’s eye effect sometimes seen in gemstones such as chrysoberyl, apatite and tourmaline is known by the technical name of chatoyancy. The effect is caused by tiny parallel inclusions that give the appearance of a narrow line similar to a cat’s eye. Often a gemstone needs to be viewed in natural light to see the chatoyancy effect.
A chip is a shallow opening on the surface that is the result of damage that occurs after cutting.
A timepiece that, in addition to the normal time telling function, also performs a separate time measuring function such as a stop watch – with a separate seconds hand which can be started, stopped and reset to zero via push-buttons on the side of the case.
Chronometer (or Chronometre U.K.)
A highly-precise timepiece which, after rigorous testing, has received a timing certificate from the official Swiss timing bureau Controle Officiel Suisse des Chronometres (COSC). (Greek for Chronos=time/Meter=measure).
Any process used to improve the apparent clarity of a diamond. This is a relatively complex subject… please refer to the following page on the subject- Clarity Enhanced Diamonds.
Clarity, Diamond Clarity
Diamonds have internal features, called inclusions, and surface irregularities, called blemishes. Together, they’re called clarity characteristics. A diamond clarity grade is determined by the relative absence of clarity characteristics. The Diamond Clarity Grading System was developed by GIA (Gemological Institute of America) in 1953 and is now the common international language when we talk about diamond clarity. The 11 diamond clarity grades are as follows-
A trade term to refer to a diamond that relatively free of any inclusions… typically a grade of SI1 or higher. It is not a standardized term, so one person’s clean diamond is another person’s not clean diamond. It is a term that is prohibited by the American Gem Society for use by its members. It is also prohibited by the Federal Trade Commission, unless the diamond meets the FTC′s definition of the term perfect. There is another term “Commercially Clean” which would be a grade lower than “Clean”, about SI2 to I1…. again, this is not a standardized term.
The property of some crystalline minerals, such as diamond, to split along certain planes when struck by a blow. These cleavage planes result in a clean flat surface that looks very much like they are a polished facet.
A break parallel to a cleavage plane. It is characterized by a two-dimensional nature; intersections with facets are usually straight lines. It is generally the most dangerous characteristic in a diamond, if it is present, since it could affect the durability as well as the diamond’s beauty.
A culet, the small facet on the bottom of a diamond, that is too small to be resolved with the unaided eye and that can be seen only with difficulty under 10x magnification.
A trade term used to designate a small table diameter. However, its interpretation and use varies. It may refer to a diameter less than the American cut 53% (of the girdle diameter) or, more frequently, to a table smaller than about 60%, because so many of the stones cut today have tables well over that 60% figure.
A group of extremely tiny inclusions that are too small to be distinguishable from one another, even under high magnification. The result is that, under a microscope, this grouping often looks like a soft transparent cloud inside the diamond. Wow…. a cloud inside of your diamond!, cool!!!
A type of diamond setting with many diamonds in a single group.
A diamond with a surface coating which masks the true body-color. The coating may be extensive (entire pavilion, for example), but is more often limited to one or two pavilion facets or a spot on the girdle.
Color Change (gemstones) Color change gems change color due to changing light conditions (such as alexandrite or color change sapphire) or when viewed from different angles (such as andalusite or iolite).
Determining the body color of an unmounted (loose) diamond when compared to the known colors of a “master set” of diamonds. This needs to be done under a controlled lightning environment by someone who is trained in the grading system.
A determination of the cause of color in Natural Fancy Color Diamonds. Diamonds that are naturally colored are very rare and expensive. Fancy Diamonds are also available as Color Enhanced Diamonds, where the color has been induced by artifical means. A Gemological Laboritory is able to determine the cause of the color in a Fancy Color Diamond.
Color Used in the evaluation of a gem. The quality of a gem can based on either the presence or the absence of color.
All natural gemstones other than diamonds.
A French commercial diving company (COmpagnie Maritime d’Expertise), which in the 1960s, aided in the development of the one-way gas escape valve in the Rolex Sea-Dweller.
Any additional function the wristwatch performs beyond basic time telling (i.e. hour, minute, and second), such as date, day of the week, moonphase, perpetual calendars or even stop/start chronograph functions.
Concave Cut Traditional gem facets are flat or two-dimensional. Concave cutting creates facets that are curved or three-dimensional. These curved facets refract more of the ambient light and return it to the eye as brilliance. Concave cutting is a recent innovation dating back to the early 1990′s. It requires considerable expertise and results in higher weight loss to the rough stone, since more material must be cut away to create the curved facets.
Clasp used, whereby the buckle is concealed under the bracelet’s links, giving appearance of a continuous flowing bracelet This clasp is found on Modern Rolex President models.
A crystalline form of aluminum oxide known in the gemstone world as ruby and sapphire. It is naturally clear, but can have different colors when impurities are present. Corundum is much admired for its hardness (9.0 on the Mohs scale) and brilliance and excellent wearability.
COSC (Controle Officiel Suisse des Chronometres)
Official Swiss testing station, whereby watches are tested for the chronometer rating.
A Rolex trademarked term, which is similar to the chronograph, the cosmetic difference being that the tachymeter scale is printed (or engraved) on the bezel rather than on the outer rim of the dial.
Counterfeit Rolex Parts
Any aftermarket parts that bear illegal, fake or otherwise non-authentic Rolex trademarks, logos or hallmarks. These parts are used with the sole intention of deceiving someone by misrepresenting the watch/parts as authentic Rolex made.
The largest angle measured from the normal at which light can escape from and optically dense substance, and the smallest angle to the normal at which light is totally reflected within the dense substance. Pretty simple, huh!
The upper portion of a faceted diamond, which lies above the girdle.
The angle of a diamond’s bezel facets (or, on emerald cut diamonds, the row of concentric facets) as measured from the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light coming up from the pavilion exits the diamond in the crown area… exiting at different angles which breaks up the white light into its spectral colors, creating a beautiful play of color inside the diamond.
Crown Guards (Also Shoulders)
Protective rails protruding from the watch’s case on either side of the crown for the purpose it from damage.
The height of the diamond that is above the girdle. Measuring from the girdle to the table facet.
Crown Height Percentage
The crown height expressed as a percentage of the average girdle diameter of a Round Brilliant Cut diamond or the width of a Fancy Cut diamond.
A crystallographic system, the crystals of which may be described by reference to their axes of equal length, each situated perpendicularly to the plane of the other two. Diamond belongs to this system. Another bit of useful information!
A lab created diamond simulant, often abbreviated as CZ. While CZ is a transparent stone, trace elements can be added to the manufacturing process, producing a wide range of colors. On Mohs scale of hardness, CZ is harder than other gemstones except for diamond, ruby, sapphire and chrysoberyl. Not to be confused with Zircon, a natural gemstone.
The lowest part of a gemstone. This looks the tip or point of the stone.
Squared shape with rounder edges, used on older model watch cases.
Cushion Cut Diamond
A square or rectangular shaped brilliant cut diamond with rounded corners. The overall shape is similar to a pillow or cushion. It is a modern version of an Old Mine Cut diamond.
Cut refers to the angles, symmetry, and proportions a diamond cutter uses in transforming a rough diamond into a polished diamond. One of the 4Cs used to evaluate a diamond, see Diamond Cut
Cutting Style or Faceting Style
This refers to the shape, size, and arrangement of the facets on a diamond. It can be categorized into the following three basic types.
Glass bubble positioned over the date aperture for the purpose of magnifying the date to be more easily read. First patented on May 1, 1952, and publicly released on the datejust at the Basel fair in 1954.
CZ (Synthetic Cubic Zirconia)
A widely used diamond simulant. See Diamond Simulants.