Sunday, June 5, 2011

Gemstone Treatments

Though not commonly known to the public, many gemstones are treated in some way to enhance their color and clarity.  These treatments are common and widely accepted in the industry, and normally do not de-value the stone.

Most retail jewelers do not divulge this information to their buying public and sometimes they themselves are not aware of it.  If they are a reputable and ethical establishment, they will be honest if queried on the subject.  Don't expect this information to be offered without inquiring first.

The most common treatments used on natural stones that I have come across are listed and explained here.

Heat treatment is the exposure of a gem to high temperatures to alter its color and/or clarity.  This is the most common method used to color enhance gems.  The most common gems that use heat treatment are:  amber, aquamarine, amethyst, citrine, ruby, sapphire, tanzanite, topaz, tourmaline and zircon.  Heat treatment is considered durable and permanent under normal handling conditions.   The heat may render the gems slightly more brittle than usual, so care must be taken not to damage pointed faceted corners and edges.

Dyeing introduces colored dyes into porous or fractured gems to change their color. Such fractures are sometimes purposely induced by heating the gem so that an otherwise non-porous material can more readily accept the dye.  The most common gems that are dyed are:  pearls, coral, turquoise, lapis, howlite, nephrite jade, chalcedony, quartz, emerald, and ruby.  Dyed gems can be quite durable, but is ultimately dependent on the stability of the dye itself.  Many dyes can be removed if the gem comes into contact with a solvent such as alcohol or acetone.  Some dyes are unstable with exposure to the ultraviolet in sunlight and can fade over time.  The best treatment for dyed gems - care must be taken to not bring them in contact with chemicals such as acetone or alcohol, which could dissolve the dyes, or have them exposed to prolonged periods of sunlight (such as leaving it on a sunny window ledge) which could cause the dyed colors to fade.

Surface Coating alters a gem’s appearance by applying a coloring agent like paint to the back surfaces of gems (a treatment known as “backing”), or coating the  gems surface with such enhancements as lacquering, enameling, inking, foiling or sputtering of films to improve appearance, provide color or add other special effects.  The most common gems that use this treatment are:  diamonds, tanzanite, topaz, coral, pearls, and quartz.  Coated gems tend to have a softer surface and/or the coating may not adhere well to the underlying gem.  These thin-film surface coatings are susceptible to scratching, particularly along facet edges and junctions.  Do not allow any hard or abrasive objects to come in contact with coated gems.

Impregnation stabilizes porous gemstones using a colorless bonding agent, such as polymer, wax or plastic, to add durability and improve appearance.  The most common of these gemstones include:  turquoise, lapis lazuli, jadeite, nephrite, amazonite, rhodochrosite and serpentine.  Many impregnations are often “skin deep” and due to the melting point of plastic and wax, can be susceptible to heat damage. Plastic impregnations are considered durable in gem materials such as turquoise as long as they are not subjected to heat or chemicalsCare must be taken not to subject gemstones with wax or plastic impregnations to heat, such as that encountered by a jeweler’s torch, since these will likely melt the material.

Irridation uses neutrons, gamma rays, beta particles or high energy elections to alter the color of gemstones.  This is sometimes followed by a heat treatment to further modify the color.  This second step also known as a “combination treatment.  The most common gems that use this treatment are:  diamonds, corundum, topaz, pearl, quartz, some varieties of beryl and spodumene.  Some irradiated gems’ color fades upon exposure to strong light.  Blue topaz, diamond and quartz tend to have very stable colors as long as they are not exposed to high temperatures.  Irradiated colored diamonds' colors may be damaged if the diamond is exposed to the heat of a jeweler’s torch.  In the beryl and spodumene gemstones, the irradiated color tends to be short lived and fades upon exposure to bright light.

Fracture or Cavity Filling is filling surface-reaching fractures or cavities with a glass, resin, wax or oil to conceal their visibility and to improve the apparent clarity of gem materials, appearance, stability, or in extreme cases—to add to a slight amount of weight to a gem. The filling materials vary from being solids (a glass) to liquids (oils), and in most cases, they are colorless (colored filler materials could be classified as dyes).  The most common gems that use this treatment are:  diamond, ruby, emeralds, quartz, aquamarine, topaz, tourmaline and other transparent gems.  Durability?  Much depends on the filler. Glasses tend to be harder and therefore more durable than resins, oils or waxes. Changes in air pressure, proximity to heat, or by exposure to chemicals can all affect the appearance of filled gems by potentially altering or removing the filler substance.

Diffusion uses chemicals in conjunction with high temperatures to produce color and/or asterism, or star like, producing inclusions as in the star sapphire.

Bleaching is using a chemical to alter or rid a porous gem of all of it's color.  Some gemstones are bleached and then dyed, a form of “combination treatment.”  Jadeite jade, pearls, coral, chalcedony and tiger’s eye quartz may be bleached to lighten their color.

Oiling and/or Resin Infusion is filling the surface of breaking fissures in gems with colorless oil, wax, resin or other colorless substances, except glass or plastic to improve the gemstone's appearance.

Waxing is the impregnation of colorless wax, paraffin and oil in porous, opaque or translucent gemstones to improve appearance.

There may be more ways in which gemstones are treated to enhance their color and durability.  These are the more common ones I have come upon as a gemstone buyer.  If possible, try to purchase untreated gemstones.  Know that because they are more rare, they will also be a higher price than treated gemstones.

(Information for this article has come from 2 sources: from the blog Unicorn's Garden and the GIA website)

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