Man is always trying to improve things that nature has created and gemstones are no exception. Gemstone treatments go back to ancient Egypt when they would throw agates into hot oil baths in order to quench crackle them and give them a different appearance. However, in today's world, with all of the scientific advancements that have occurred, gemstone treatments have gotten far more sophisticated and far harder to identify.
Some gemstones, like tanzanite, would not even be sold if it weren't for the treatments. Tanzanite comes out of the earth a pretty ugly brown color. It is only through heat treatment that the beautiful blue/purple color it is known for appear. Similarly blue topaz, while occasionally occurring naturally in blue, would never have gotten so popular if it were not for the irradiation/heating treatment that turns the excess of white material into blue.
Some treatments are less stable than others. Emeralds have always been oiled, or more recently fracture filled with an assortment of substances, in an attempt to reduce the visibility of the inclusions, or "jardin" that is common in almost all emerald material. Oil can leach out over time from normal wear and tear (washing your hands, exposure to cleaning agents, etc.) and the entire look of the stone can change over time because of this. Advancements in gemstone treatments (not all of which are completely ethical, especially if not disclosed at the time of purchase) led to diffusion treatments of many sapphires (along with some other gem materials). Diffusion treatments are a process in which other elements are either intentionally or accidentally forced into the stone through extended heat treatments. The problem with many of these stones is that the treatment leads to a change in color that is often only on the surface. If it becomes necessary to repolish the stone for some reason, the color underneath is completely different.
If only the very wealthiest people were interested in gemstones, than it wouldn't be necessary to treat many of these gem materials. But we're living in an egalitarian society now and everyone feels they should have the right to own a beautiful stone (fortunately, since I wouldn't be in business if that wasn't the case). There is far more demand than there is supply for the finest examples of some gem materials, hence the need for treatments to enhance the natural beauty of the gemstones coming out of the earth.
My next posting will discuss sapphire treatments.
Pictured above: Natural color fine cornflower blue sapphire.