Heat Treatment of Gemstones.

Gemstone Enhancement by Heat Treatment.

Enhancing the Gemstones by heat.

The ruby burner of Chanthaburi.

In the last two hundred years inserting resin into cracks under high pressure and synthetic stones were added. The idea is always the same to improve the appearance to get higher prices when selling

Since they are too sensitive to go through this procedure only a small part was found to have the clarity and sufficient size to make them usable. All this is somehow nothing but cheating the buyers because after a couple of years this add on material will deteriorate and the pretty thing become worthless.

Especially in Thailand it needs to be very careful since the people usually don’t think must what will happen tomorrow. Actually the country is the biggest exporter of this stones and most of this gemstone heat treatment or enhancement is done in Chanthaburi.

Although some treatments have been practiced for centuries (especially heating), modern technology allows more changes as in the past. People draw the line between acceptable handling in favor what brings more money; most don’t care about the customer’s problem after some years. This fact needs attention and being very careful when buying. In every city where the gems are traded are labs to have the stones tested for relatively low prices.

The current ruby heat treatment process in use is based upon that patented by the Union Carbide Corporation in 1975.

Ruby Heat Treatment.

To the normal buyer gem materials such as ruby and sapphire appear to be absolutely solid impregnable fortresses. However, this is but an illusion, for if an object is of small enough size, as with certain atoms, it can pass through a gem as easily as sand through one's fingers. The process whereby atoms may move through a material is termed diffusion and is responsible for a number of the different changes in corundum subjected to heat treatment.

When a crystal is heated, interatomic spacing increases by an amount proportional to the temperature reached, making it possible for atoms to move, or diffuse, through the structure. Atoms of a small size, such as hydrogen or oxygen diffuse rapidly through corundum. Thus, color changes involving these elements; can be effected throughout the entire gem in as little as a few hours by heating gemstones under the proper treatment.

However, the diffusion of transition metal coloring agents, such as iron, titanium and chromium, is far slower, so even heating the gem at 1800°C for several days will produce a movement of only half a millimeter or less diffusion of atoms by means of heat treatment has been applied to rubies and sapphires on a commercial basis for the past several years with the aim of imparting a thin layer of color at, and just below, the surface.

To do heat treatment of Precious Stones for a better look.

To do heat treatment for a better look, colorless to lightly colored corundum gems are readied for treatment by preforming and cutting, but not polishing, as this inhibits the diffusion somewhat. They are then embedded in a crucible containing a powder that consists of alumina, titanium and metallic oxide colorants. Alumina itself has no effect, while the titanium aids surface penetration and lessens the formation of color bands.

The coloring agents used are generally the same as those employed for doping synthetic corundum. Now the crucible is heated to between 1600 and 1800°C for up to 200 hours. This allows the atoms within the powder to diffuse into the surface areas, creating a thinly colored skin which, after a light repolishing, is rarely deeper than a few tenths of a millimeter.

Natural rubies and sapphires.

Thus, natural rubies and sapphires in which the color is too light, or uneven in distribution, can be treated by the above method to correct these deficiencies. Due to the relatively large quantities of clean lightly colored sapphires available from Sri Lanka, this material is most often used for surface diffusion treatments. Stones from other localities may also be used, but less frequently.

In terms of the colors produced, the majority are blues, with some rubies (reds), padparadsehas (oranges) and yellows also being treated. When the process is done properly the colors resulting from surface diffusion can be nearly equal to nature's finest efforts.

Diffusion-Treated gemstones.

However, because the coloring agents have been artificially induced into the gems, and because they are only at the surface, diffusion-treated stones have not been accepted by the trade in the same way as those involving heat treatments alone.

Thus, it is imperative that gemologists are able to identify these stones. A visual inspection of diffusion-treated gemstones yields comparatively little of use with regard to their separation from untreated stones.

Deeply colored pieces may at times appear slightly darker around the girdle, because of the concentrations at the surface.

There is a general agreement that non-permanent treatments such as irradiation, surface diffusion and repair, oiling and dyeing should be disclosed. However some would draw the line at permanent treatments involving heat.

Opponents to the disclosure of permanent gemstone treatments feel that it is unnecessary and will confuse the customer, eventually hurting business. They believe that so long as a treatment is permanent there is nothing to worry about; the whole controversy is so much needless fuss generated by a group of consumer witch hunters.

Is it neatly, though? The most important factor in maintaining the value of precious stones is the rarity. To see that this is true we need only look to synthetic corundum. A synthetic ruby / sapphire produced by the Verneuil method is a gemstone in every sense of the word, with the same hardness, durability, color permanence and beauty as nature's own. However, because it is produced in almost limitless quantities, its cost is but pennies per carat.

The major factor separating it in price from the natural stone is a rarity, and should deposits of natural ruby be discovered which yield quantities similar to the synthetic production, we could expect that its price would also drop to a similar level. Fortunately for those who own or deal in natural rubies, this possibility is remote, at best. The additional quantities of ruby and sapphire produced by treating inferior material also have an impact on supply and therefore price. However, since the amount of treatable rough is limited, this impact is also limited. The heat treatment of yellow and orange sapphires from Sri Lanka was not widely practiced before 1981. Before this, a fine, naturally colored, deep-yellow/ orange sapphire from Sri Lanka of 5 carats fetched $400 a carat, or more, at the wholesale level. Today, the same stone would bring only a fraction of that amount because it must compete against heat-treated Sri Lankan sapphires.

It is unfair competition, to say the least, for the treatment process yields deep-orange-yellow colors with unnerving frequency, hues that were almost unheard of before 1981. If, however, a distinction were to be made between natural and treated gems, it could be sold for what it is: a rare, naturally colored, deep-yellow Sri Lankan sapphire.

Many of those involved in treating or selling treated rubies and sapphires fear that prices for these stones would fall should they be sold with a 'color-enhanced' label attached. This seems unlikely, as supplies of treatable rough are limited. Studies undertaken in the United States by the trade magazine Jeweler's Circular—Keystone have also shown that if consumers are offered a choice of either a naturally colored sapphire or a heat-treated sapphire of similar quality but lower in price, many will opt for the treated stone.

Why heat-treated ruby and sapphire disclosure of such treatment should made public.

When heat-treated ruby and sapphire disclosure of such treatment are made public it would have note much impact. Instead, the entire gem and jewelry business will benefit from the increase in value of naturally colored gems. Perhaps of even greater importance, by the total disclosure of gem treatment jewelers will no longer have to incur the wrath of a customer who learns that their new ruby or sapphire has more likely than not been heated to improve the color. Gemstone treatments can only help boost sales in the long run actually ruby heat enhancements is already somehow normal today.

The job involves the creation of the most beautiful gem possible and, at the same time, recovering the maximum amount of weight from the rough, an enormously difficult proposition when bearing in mind that each of these ideals can only be achieved at the expense of the other.

Thus, success for the lapidary is measured in terms of an ability to strike a delicate balance between beauty and size. When working with costly materials such as ruby and sapphire, particular attention must be given to retention of weight. Because of pressures to squeeze every last point from the rough, cutters may be forced to retain small surface defects, such as pits and cavities. it is simply a case of the lesser of two evils, for although grinding the defects away completely will make the gem more attractive, this improvement is often e not enough to offset the loss in weight that results. Thus, the presence of surface pits should not indicate a lack of skill on the part of the cutter, but to serve as evidence of the difficulties in turning a profit within this highly competitive business.

Competition is of course vital to the well-being of any business, for it is what fuels the search for a better mousetrap. However, not everyone plays by the rules. During the first six months of 1985, gemologists in both London and Bangkok discovered rubies in which the surface blemishes had been filled in with transparent colorless glass. Dubbed “surface-repair’ which represented a new method of dealing with an old problem. However, the treatment not only reduces or eliminates the visibility of surface defects, but also increases the weight of the stone at the same time. As a result, it cannot he considered an acceptable treatment, and it is important that the trade is both aware of, and able to detect, this latest charade.

To date, the vast majority of surface-repaired stones encountered have been rubies, with a handful of blue sapphires also turning up. However, there appears to be no reason why gems other than corundum could not be treated in a similar manner.

Details regarding the actual method of treatment were recently supplied to the author by someone who had talked to a man performing a surface repair on rubies.

Heat Treatment of Sapphires.

E.g of yellow sapphires from Sri Lanka and claimed to be the first person in Thailand to treat rubies by surface repair. According to him, surface repair involves applying a silica-based gel to the surface of cut stones with a paint brush in the areas to be repaired. The stones are then heat treated, turning the gel to glass and fusing it into the pits and cavities in the process. He claimed that his surface repair jobs were superior to all others as the glass adhered tightly to the surface and did not fall out like those of other burners.

It should be mentioned that the idea of filling in surface cavities with a foreign substance is not totally new to the trade. In the past, a number of different materials including epoxy and doping shellac have been used to hide unsightly defects, particularly on cabochon-cut stones. Patents have also been taken out on processes very similar to surface repair, such as those for the glossing of corundum and spinel rods The detection of surface-repaired rubies and sapphires can be readily accomplished by noting the following factors:

I. The difference in luster between the glass filling and the surrounding corundum under an overhead light.

2. The difference in relief between the glass (refractive index 1.52) and the corundum (refractive index = 1.762-1.770) when immersed in methylene iodide.

3. Inclusions of spherical gas bubbles within the glass filling.

4. The colorless nature of the glass filling