Because most emeralds are highly included, they are very often subjected to a variety of treatments to enhance their visual appeal. Emerald treatment consists of numerous types of fillers, impregnations, and dyes. The purpose of which is to make the Jardin, a French word for garden used to describe the lovely inclusions one encounters in an emerald, more pleasing to the eye.
To begin an emerald treatment or retreatment, as almost all emerald enhancements can discolor or cloud with time, you must first clean the stone thoroughly. The cleaning process is most effective under warm conditions, not boiling. Obviously if you boil the stone or immerse it in boiling hot liquid, you can crack or shatter it. If you warm both the stone and the liquid used to clean or to fill/penetrate the emerald together, you will open the pores of the stone, allowing deeper penetration.
Cleaning can consist of a simple soaking overnight with the stone in a jar of the cleaning medium on a hot plate. You can use organic solvents or, for a more vigorous cleaning, acids. Organic solvents that are safe to use with emeralds include acetone, methyl alcohol, ethyl alcohol, and Attack, a methylene chloride solution used to dissolve cured epoxy and polyester resins. You might want to use a covered container, as these preparations can evaporate in air and leave a residue worse then the original problem.
If you find the solvents do not remove the contaminants you can use acids. Hydrochloric acid, also called muriatic acid, is safe for cleaning emeralds. For an intense cleaning, try aqua regia, a mixture of one part by volume concentrated nitric acid with parts concentrated hydrochloric acid. If your emerald has orange or brown rust stains, you can remove them with a solution of oxalic acid.
Exercise caution when using and disposing of these acids. After the acid treatment a washing with soap and water, and in some cases a bath in a neutralizing solution, is required. Some acids can have a delayed discoloring chemical reaction so they must be neutralized in solutions of say, baking soda and water. Consult a mineral cleaning expert for details.
(Editors note: See Cleaning Care and Maintenance of Gem Stones for more information.)
Once the stone is cleaned well and allowed to dry thoroughly you can simply soak it again on a hot plate in your filling/penetrating solution overnight or, a more effective method, is to place the stone in a vacuum and insert the treatment medium while still under the vacuum. Again, all of this is done under mild heating to open the pores of the stone, drive off any remaining water, and in some cases, to keep the medium material liquid.
A simple chamber can be constructed inexpensively using a plastic or glass bell jar type cover, a hot plate and hydraulic piston assembly. You can obtain a bell jar cover at a casting supply and the parts to construct the hydraulic force feed can be obtained from you local auto supply. Here is a picture of an assembly:
To determine the substance you should use to treat your emerald, you need to consider several factors. First, you need to decide exactly what you want to treat the emerald for. If you want to disguise cracks and inclusions, you should use a material close to the refractive index of the stone. If the stone has pits or fissures that break the surface you may want to use a thicker filling agent. In the case of a pale or color-zoned stone, you might consider a coloring additive to give the gem a richer, more even color. To color the emerald you can use any number of dyes, including chromium powder, and a ready mix that contains both the oil and dye. This ready mix is sold in Bangkok under trade name of “Crown of King” emerald oil. If you permeate the emerald with chromium powder it will give the added effect of a nice red glow under an emerald filter or ultraviolet light. A chart of the refractive indices of various common treatment mediums and lists of commercial treating companies, sources of equipment, and chemicals is available at the end of this article for reference.
Here are some tips and information about the long-term effects of the more common mediums. First, although there has not been extensive testing, irradiation appears to have no effect on emeralds. Crystals from Columbia, Scandium, and Australia were irradiated both in natural crystals and after a bleaching to white by heating to destroy the color centers. One would expect emerald on irradiation to at least go yellow, the common result on irradiating most beryl. But again, limited experiments produced no change.
For those who are considering using a laser, it will remove the black spots, but it also leaves a black trail where the laser burns through the stone. The emerald holds up to the lasering, but it shatters in the heated acid bath that is used to clean up the black trails. One of the most common emerald treating substance is cederwood oil, which discharges quite rapidly and a thicker application will not delay this effect. Also, when exposed to ultraviolet light cedarwood oil emits oxygen as a by product which can stain.
Canadian Balsam, Abies balsamea, is an oleoresin obtained from the North American balsam fir. It is an excellent filler due to its thickness, even in a liquid state on heating; however, this is an organic material and can decay and discolor over time. This can be delayed or forestalled and the material thinned for better penetration by addition of chemicals such as toulual. Canadian balsam is also used as an adhesive to hold laboratory microscope slide covers. It is often sold ready mix by chemical houses with additives to preserve it against this deterioration.
Opticon, a lapidary fracture filler, works well with the drawback that the sealer used with it breaks down after a year and begins to oxidize and change to a yellow color. It has an advantage over some others that when set up it is hard enough to polish. Palm oil or Palma, a synthetic derivative of Epoxy 828 or 6010, has the disadvantage of clouding to a milky color in the long term.
An excellent filler similar to the “Yehuda” method used in diamonds, is the solder glass used in the electronics industry with melting temperatures of 250 C. A colored glass can also be used.
One of the simplest fillers, and one that gives an excellent finish, is bees wax. You can apply it after all treatments or by itself to fill minor pits and to give an excellent luster to the stone.
Vaseline or mineral oil (liquid paraffin) are quite long lasting and will not discolor. Water glass, (sodium silicate) is an excellent filler, does not discolor, and is hard enough to polish.
Epoxy No.224 plus hardener turns yellowish orange in the long term. Dental fillers and epoxy based adhesives that set up with ultraviolet light are of mention because they appear not to discolor. Of note is a patent applied for process “Gemtrat” of epoxy resin and hardener by the firm Arthur Groom. It is stated to be permanent and not discolor.
|Coconut oil, paraffin wax||1.45||Quartz||1.55|
|Neat’s foot oil, whale oil, Corn, mineral, olive, peanut||1.46||Beryl, Emerald||1.58|
|Rapeseed & soybean oil||1.47||Topaz||1.61|
|Caster oil, linseed oil||1.48||Ruby, Sapphire||1.77|
Commercial Emerald Treaters Robert Linder. Specialize in Oiling and Opticon. Lindeau Gems, 150 E. 49th St., Suite 1B, New York, NY 10017 Ph 212-759-8404 Fax 212-759-8361
Arthur Groom & Co. “Gemtrat” Epoxy resin + hardener Ph 212-832-9100 Fax 212-832-9124 Email [email protected]
Laboratory Equipment Fisher Scientific 809-738-4231
City Chemical 212-929-2723
Mark Liccini LICCINI Gemstone Rough Dealers since 1970