Posted on November 28, 2012
TEN TYPES OF GEM TREATMENTS THAT YOU SHOULD KNOW BEFORE START BUYING GEMSTONE
Gem treatment is any human-controlled process that improves the appearance, durability, or value of a gem
This broad definition does not include basic fashioning techniques, such as faceting, cabbing, or carving.
It does include those processes that create disclosure problems. Here are list of treatment that most commonly use amongst people in the gem industry that you should aware of before start buying gems.
1.) BLEACHING, a chemical lightens or removes color (or dark inclusions).
Pearl and other delicate materials, like ivory, will bleach under exposure to light and bleaches, like hydrogen peroxide.
Diluted acid or straight chlorine bleach can lighten tiger’s-eye, jadeite, and some chalcedonies.
Stronger solvents can lighten or remove diamond inclusions. It’s common to bleach dark inclusions in diamonds after laser drilling a channel to reach the inclusion.
2.) CAVITY FILLING, Treatment that fills and seals voids to improve appearance and add weight.
Generally speaking, surface-reaching cavities, pits, and other depressions often make a gem less desirable. Cavity filling serves a number of purposes.
Treatment specialists have used cavity filling on tourmaline, opal, and emerald with varying degrees of success and frequency. Generally speaking, the treatment appears more often in rubies and sometimes sapphires than other gemstones. Detecting filled cavities of large fracture can be fairly easy in most case as there’s a big difference in the luster and hardness of host corundum and that of the filler. So a gemologist, can detect large filled cavities by looking for luster different on the luster gemstone surface.
3.) COLORLESS IMPREGNATION-Filling of pores or other openings with melted wax, resin, polymer, or plastic to improve appearance and stability. Since, skin oils or other chemicals often discolor untreated porous gems like turquoise, lapis lazuli, and jadeite. Treating them with colorless substances such as melted wax, polymer resin, or plastic can seal such gems and improve luster.
The same treatment can also turn a pale turquoise to a bright blue. However, if dye is added to the filler, consider the treatment both impregnation and dyeing.
4.) DYEING is a treatment that adds color or affects color by deepening it, making it more even, or changing it. Dyeing is the opposite of bleaching. The purpose is to add color or affect an existing color by deepening it, making it more even, or changing it. The process generally involves exposing a material to a chemical. To accept dye, the material must be porous, like Jadeite, chalcedony, Lapis Lazuli or have fractures that reach the surface. Without any of those properties, it is unlikely that dye can alter the gemstone color. Quench-crackling, a process that combines heat with rapid cooling can produce the necessary fractures. Most commonly dyed gems include lapis lazuli, jadeite, cultured pearl, quench-crackled rock crystal (to imitate other gems), howlite, magnesite and turquoise.
5.) FRACTURE FILLING is a process in which filler is used to conceal fractures and improve the apparent clarity of a gem. The process involves filling fractures that reach a gem’s surface. As with cavity filling, these treatments use a variety of fillers, like plastic, glass, polymer resins, and oil. Canada balsam, cedar wood, and palm oils are among the wide variety of fillers used. Sometimes the stone just soaks in the filler. And quite often that fillet is gently heated first so the filler becomes more fluid and easily getting into gem’s fracture.
Most of the fillers in this category are colorless. If they’re at all tinted, that could negatively affect the gem’s color. If a dye is added to the filler to affect the gem’s color, the treatment becomes both dyeing and fracture filling. Emerald, ruby, and rubellite tourmaline are amongst one the most commonly fracture-filled gem.
6.) HEAT TREATMENT is the method which exposing a gem to rising temperatures for the purpose of changing its appearance. This is one of the oldest and most common of treatments. Examples of heat-treated gems were found in the tombs of ancient Egyptian kings. The Egyptians heated white chalcedony to an attractive orange color, creating the variety carnelian. Today, a growing understanding of gem chemistry has led to sophisticated heat-treating processes. In general the effect of heating is stable for many gems under normal wear. Gemstones that are commonly heated include ruby, sapphire, aquamarine, tanzanite, amethyst, citrine, Apatite, and etc.
7.) IRRADIATION-involve exposing a gem to radiation to change or improve its color. Experiments in gem irradiation began in the early 1900s. Today, irradiation is used routinely to treat a wide range of gemstones. Irradiated stones might have traces of radiation, but it’s seldom harmful.
8.) LATTICE DIFFUSION is a very slow process involving heat and chemicals. Material, such as corundum, is heated to near its melting point. The high temperature allows the chemicals to penetrate the surface and become part of the crystal structure. Usually the chemicals are natural components of the gem material. Sapphires, for example, are often heated with a mixture of alumina (Al2O3—the basic recipe for corundum), titanium oxide, and iron oxide to get blue.
9.) SMOKE AND SUGAR treatments are surface treatments used to darken opal and bring out its play-of-color.
Of these two processes, sugar treatment is the more common.
Smoke treatment involves wrapping a similarly low-grade opal in paper (sometimes soaked in motor oil) and roasting it.
10.)SURFACE MODIFICATION-Altering a gem’s appearance by applying backings, coatings, or coloring agents like paint. The coating substance doesn’t become part of the treated gem’s crystal structure. Surface modifiers vary widely in sophistication. The three basic typs of surface modification are: Backing , Coating, and Painting. From 2000 BC to the eighteenth century, the world commonly accepted backing treatments that added color or created phenomena like asterism.