Enhancement, when used in gemological conversation, stands for a man-induced treatment which improves the appearance or durability of a gemstone.
Gem minerals are rare, durable and beautiful by definition; this is what distinguishes them from all other minerals. Most gem deposits do not solely yield gem grade stones though. In fact, every gem miner will be able to tell you that only a small percentage of the stones he unearths is fit for jewelry. There may be too much or too little color in the stone, the color may be of an undesirable hue or it may be fractured or unstable. Since the demand for gemstones always outweighs the supply, causing their high prices, this is where these non gem grade stones become economically interesting. If a miner can offload his lower grade stones as well as his prime stones his business has got a much better chance on surviving.
Because the natural, untreated product is extremely rare, high prices are commanded throughout the line of production from mine to consumer. Non gem grade stones that are fit for treatment are in greater supply and don't enjoy this natural rarity to the same extend. They can be bought cheap from miners keen to cash their low quality stones so consequently should command lower prices. Relatively inexpensive treatments are then performed to make the stones look exactly like the popular natural product. All too often it takes an expert to distinguish between the natural and treated stones. Now here's where problems may arise. This resemblance makes it possible for unscrupulous dealers to sell the treated product as natural and command top dollar. The proper way to deal with these stones is to disclose the treatments properly.
The price difference between natural and treated goods isn't solely a rarity factor. In some cases the enhanced stones resemble the natural product in appearance but not in durability. A glass-filled ruby for instance isn't as resistant to abrasion and chemical attack as the real deal. This is another reason proper disclosure is of the utmost importance, things that wouldn't affect a natural stone may ruin a treated one.
So, are treatments an evil thing? The answer is no, not when they are properly represented as being treated in one or the other way. The increased prosperity that occurred over the last century allows far more people to indulge in wearing gemstones. Where gems were reserved for the nobility and wealthy in the past, now billions of people have surplus income and are happy to show that off by wearing expensive personal decoration. The demand for gemstones is so big these days that without gem treatments the prices for natural goods would go through the roof.
Treated goods have become an essential part of the jewelry trade. Consumers need them in order to meet their increased demand and the miner needs them to make a consistant living. Without the selling of treatable stones he would be left at the mercy of his luck of finding a gem grade stone every day. It is estimated that 80% of the worlds gemstones are mined by independent artisanal minersand it is important that this group can make a decent living. Without these hard working souls these beautiful gifts of nature wouldn't reach you.
And for the jewelry historian? To those investigating the age of a jewelry item treatments may provide very helpful clues. We have a reasonable good idea of the invention dates of the different treatments and finding a stone which is clearly treated in a way that was invented in the 1970's in a Victorian jewel should raise alarm bells. The stone may either be a replacement of an old stone or indicate a recent reproduction. Either way a closer look is at place in such cases and spotting a modern treatment may contribute to the correct identification of a well made reproduction as such.
Below you will find all possible treatments, the gemstones which can be enhanced by these treatments together with the effect of the treatment and the supposed introduction dates of these techniques. Follow the links below to learn more about specific treatments.
|Material||Effect||Date of introduction|
|Amber||Small fractures; sun spangles
Clarity enhancement Aged look; darkening of surface
|Beryl||Eliminating the yellow color component in aquamarine||? BC|
Introducing asterism by exsolving of silk
|1960’s: Gueda sapphire to blue
(Crowningshield 1966, 1970, Beesley, 1982.)
1949, Burdick and Glenn patent
|Diamond||Annealing after irradiation to introduce color||1957 Crowningshield, G&G Winter 1957|
|Jade||Lightening or darkening of color
Introducing aged look
|Tanzanite||Changing of brown into blue||1967?|
|Topaz||Changing of color, Annealing after irradiation||1957 stable blue color product of irradiation in combination with annealing. Pough, 1957|
Recrystallization of metamict stones
|Heat + Additive a.k.a Diffusion|
|Corundum||Surface diffusion, changing color
Bulk diffusion, changing color
|late 1970s Crowningshield, 1979
Late 1990’s - 2000 Emmett et al
|Feldspar||Pipe diffusion, changing color||2008, (Milisenda, 2008, Emmett, 2009)|
|Beryl||Changing color||1947 (American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Corundum||Changing color||1947 (American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Diamond||Changing color||1914, Irradiated diamonds by immersion in radium bromide, (Pough & Schulke as reported in G&G spring 1951)
1938, Cyclotron irradiated diamonds (Hardy G&G summer 1949)
|Pearl||Darkening||1967, (R.T. Liddicoat G&G spring 1967)|
|Quartz||Changing/introducing color||1949 (G&G winter 1949)|
|Spodumene||Changing color||1947 (American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Scapolite||Changing/introducing color||(American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Topaz||Changing color||1909 irradiation of pink topaz to orange (Pough & Rogers, 1947) 1957 stable blue color product of irradiation in combination with annealing, (Pough, 1957)|
|Tourmaline||Changing color||(American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Zircon||Changing color (structure from crystalline to metamict)||(American Mineralogist, vol. 32, p 31-43 jan-feb 1947. Reported in G&G spring 1947)|
|Beryl (Emerald)||Clarity/color enhancement by (colored) oil or epoxy resin||Oil – BC
Epoxy resin – 1994 ( Levy, 1994 ICA gazette, april)
|Diamond||Glass filling||1982, Zvi Yehuda|
|Opal||Impregnation: stability enhancement||?|
|Turquoise||Impregnation: color and stability enhancement||?|
|All gemstones||Adding a colored layer||BC|
|All transparent gemstones||Adding a transparent layer with different optical density than the gem to create color by interference effects||Early 1940’s (Gubelin, G&G Winter 1949 p. 243)|
|Diamond||Improving color grade of a diamond by application of coating techniques resulting from WOII research: Vaccuum sputtering of Fluorides on pavilion or girdle||first lab alert 1952 Law enacted against undisclosed marketing of coated diamonds in 1962 by NY State.|
|All transparent gemstones||Enhancing/introducing color, increasing brilliance||Minoan times (Ball, 1950) Roman times (Pliny 76 AD)|
|All gem materials||Introducing/enhancing color||BC (Pliny 76 AD)|
|Diamond||Clarity enhancement||1970 (Crowningshield G&G fall 1970)|