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GLOSSARY OF FREQUENTLY USED TERMS

++As I was trained in grading and describing colored stones by GIA, many of these definitions are similar to or identical with theirs - some, however; are my own as are any errors herein.++

Clarity terms:

Flawless at 10x: using a 10 power magnifier and good light, no inclusions, surface imperfections or color banding can be seen.

Internally flawless: using a 10 power magnifier and good light, no inclusions can be seen, but there may be polish marks or tiny abrasions on the surface. "Almost "or "nearly" used with either of the above means that only the tiniest imperfections can be seen.

Darkfield illumination: a way of lighting a gem so that normally hard to see inclusions stand out sharply in relief. I use this lighting in conjunction with the 10x loupe in grading the stones.

Eyeclean: The stone has no visible inclusions, surface imperfections or color banding as viewed face-up, about 12-16 inches away in normal, good lighting. This is how the average person would view a stone in jewelry or a collection . For many, this is the most desirable clarity state as the stone looks great, but when viewed under magnification shows internal characteristics which can prove its naturalness or even identify its source. Since everyone's visual acuity is different there's a possibility that what I label as eyeclean might look better or worse to you. An eyeclean stone as described above might have visible inclusions if scrutinized under very bright light, held close to the eyes or turned on its side or back where reflections do less to hide inclusions. "Better than" or "almost" will be found as modifiers to the term eyeclean to indicate stones which fall just outside this designation. In some gem pictures which were taken with a magnifying closeup lens, inclusions may be visible in the photo even though the stone is graded eyeclean.

Very Slightly to Slightly Included: Stones with this designation have eye-visible inclusions which do not markedly affect either the stability or beauty of the stone. A few varieties such as emerald and rubellite almost never exceed this grade.

Moderately Included: The inclusions are grossly visible and affect the beauty and/or stability of the stone. Usually these stones are acceptable only if the material is very rare or the price is very low.

Included: Pretty much like driveway gravel. None are offered on this site.

Color Terms:

**(colors usually are relative to the range for that variety: a medium aqua would be lighter in tone than a medium rhodolite, for example)**

AAA: the best color that a stone could have for its variety. In the GIA scheme: 10/10.

AA: just one shade lighter or darker or one hue off the AAA color. 8-9/10.

Very dark: the stone looks black under most lighting conditions, only in strong sunlight or when lighted from the side or below is color seen.

Dark: the darkest shade of color without looking black under normal lighting.

Medium dark/medium: these are the tone values which, for most stones, are most desirable.

Medium light: not as dark as medium, but with good noticeable color

Light/pastel: noticeable color

Pale: only the faintest hint of color, often only noticeable against a white background

Intense/vivid/electric/neon, etc. Terms meant to indicate a richness of color that is outstanding

Saturated: This term means a color is pure, rather than being modified by grayish or brownish tones. It is NOT a synonym for deep or dark. A stone can be deep, but not saturated and saturated without being dark.

Cut terms:

Native cut: Usually this means a stone has been cut at the country of origin by lapidaries working on native style equipment. Generally the stones are windowed (to save weight) and often have little crown and very large bellies (which deepens color). Often facet meets and polishes are imperfect. Styles are usually ovals or cushions. On this site "native cut" will mean a stone with these characteristics, regardless of where it was cut or with what style of equipment.

Custom cut: This means that a stone was cut using optimal pavilion angles to maximize brilliance. It shows excellent symmetry, a well proportioned crown, good facet meets, a fine polish and no window. Occasionally a custom cut stone is deliberately windowed to show inclusions (rutilated quartz) or to emphazise color separation (ametrine) or to lighten a dark stone (almandite/iolite) In these cases, however, something other than maximum brilliance was being sought. Sometimes stones from "native" sources meet or come very close to custom specifications, in which case they have not been designated as native cut. All gems, on this site unless otherwise labelled are custom cut.

Well proportioned: a stone is well proportioned if its crown is 1/3 - 1/4 of total depth, and if its table falls between 40 and 70% of the total width.

Window: A window is an area under the table of a stone that does not reflect light. It's called a window because light goes through it like window glass. It is almost always undesirable and occurs when pavilion facets are cut below the critical angle for a gem material. To test for a window, hold a gem, face up, with the table parallel to a sheet of newspaper and look through it. If you can read the print, the stone has a window. Most native cut stones have large windows as using low pavilion angles allows a larger stone from a given piece of rough.

Barion cut: A style of cutting transparent stones invented by famed diamond cutter Basil Watermeyer and named for Basil and his wife Marion by Glenn Vargas. In essence, it's a way to bring the benefits of brilliant cutting to shapes which are usually step cut. All the pavilion facets are near the optimal angle for the gem so that maximum brilliance is obtained. Frequently the crowns of such stones are step cut. The pavilion is slightly deeper than most other cuts of the same face up dimensions, a fact which should be taken into account when planning to set the gem into a commercial mounting.

Apex: Instead of a flat table on the crown of a stone, there is a low angle dome. It's done to enhance interest, or to increase face up brilliance in a species with a low refractive index.

Buff Top: a style of cutting in which the pavilion is faceted and the crown is cabbed.

Opposed Bar: a style of crown with a series of parallel rectangular facets in place of a table and other crown facets.

Concave facets: facets that, rather than being flat, are actually depressed or sunken in. A special faceting machine that uses cylindrical cutting and polishing laps is necessary. Such facets can enhance brilliance and/or create interesting reflective patterns in the stone. Stones cut this way are generally more costly than comparable stones with regular faceting as the process is more time consuming and the necessary equipment is more expensive.

Terms used to describe Antique/Vintage and Estate Jewelry:

Antique: 100, or more, years old

Vintage: The use of this term varies widely, but on this site it will be used to designate pieces more than 50, but less than 100, years old.

Estate: Estate items are previously owned, and range from contemporary to 50 years old.

Time/Stylistic Periods:

Victorian: 1837 - 1901

Art Nouveau: 1890 - 1915

Art Deco: 1920 - 1935

Retro: 1935 - 1950

Gemological terms:

Refractive Index: (RI) is the characteristic slowing of light as it travels through a given gem species. The higher the RI, the greater brilliance and luster is possible. The fact that each gem material has its own RI makes it necessary to facet each species at slightly different angles and makes it a useful characteristic in gem identification.

Dispersion: The measure of a gem's ability to break white light into spectral colors. The term "fire" is often used as a synonym. Certain cutting styles, like high crowns can enhance dispersion. Rich body color in a stone can sometimes mask some or all of the dispersion, as in the case of Benitoite and demantoid garnet.

Luster: The ability of the gem's surface to reflect light and the characteristic appearance of that light. Adamantine luster (diamond-like) is generally considered the most desirable. Most gems have vitreous (glass-like) luster; although other possibilities range from metallic to greasy to dull. The luster on a given gem is partly due to its nature and partly due to the degree to which it has been polished.

Brilliance: The percentage of the total face up area of the stone which is reflecting light back to your eyes as you rock and tilt the stone. Brightness, sparkle, and light play are similar in meaning; fire, though sometimes misused to mean brilliance, is more properly used to describe dispersion. Well cut gems of light to medium dark colors will generally show at least 60% brilliance. Windowing (light passing through without being reflected) and extinction (retention of light within a stone) subtract from the potential brilliance. Poorly cut stones are often windowed and very dark stones can show near total extinction. Inferior polish or inclusions in the stone can also decrease brilliance.

Scintillation: The effect of reflected light being broken up into small patches which seem to "twinkle" as the stone is moved. This is mostly a function of faceting style. Brilliant cuts and many small facets produce more scintillation, large facets and step cuts less.

Pleochroism: The characteristic of a given gem species of showing a different color, or a different shade of the same color through different angles of view. Dichroic stones, like ruby, show two (orangey red and purplish red) and trichroic stones, like iolite, show three (blue violet, grey and near colorless). This property is useful in gem indentification. Pleochroic stones must be carefully oriented by the cutter to show the most desirable color, or blend of colors in the face up gem.

Bicolored, Particolored: The property of showing two or more colors in a single piece of gem material, for example, ametrine. Traditionally such stones have been cut to separate the colors, but it's becoming more common to deliberately orient the rough to mix the colors, or create a mosaic of them in the finished stone. When a stone is cut in this matter it is called "blended".

Opalescence: An effect of slight milkiness due to light scattering, seen primarily in transparent opals.

Go to: Homepage -- what's new at ACS -- monthly specials and discounts -- Barry's Custom Gemstones/Jewelry-- gem topic of the month -- gem topic archive -- birthstones -- ask Barry -- key to all the codes used on the ACS site -- definitions of terms used on the ACS site -- how to order -- about ACS -- setting these gems -- free gemology course

 -- Mail to Barry Bridgestock

 

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