Treatments, told straight

Many people think “treated” means “fake”. It does not. A treatment is a human intervention on a natural stone, carried out after mining to improve its look. Some are ancient and accepted by the whole market; others are fragile and penalising. What makes them legitimate is not the type, but one thing only: that they are declared. Transparency here is not a courtesy, in many countries it is an obligation.

Heat, the norm

The heat treatment is the most common and the most accepted. The stone is brought to a controlled temperature to dissolve veils of rutile or change the oxidation state of the elements that give the colour. Most sapphires and a large part of rubies on the market have been through the furnace. A heated stone is worth less than an identical unheated one, but the gap changes by species: on high-quality corundum it can be very wide, as we explain in the piece on reading a report.

Filling, the boundary

The fracture filling injects resins, oils or glass into the cracks that reach the surface, to make the lines optically vanish. Here the register changes with the material, and this is where the market separates honesty from deceit.

An oiled emerald follows a centuries-old tradition and is widely accepted. A lead-glass ruby is another object, and another price.

Cedar oil in an emerald is an old, expected practice, and the market allows for it. Lead glass inside a heavily included ruby, on the other hand, can make up a substantial fraction of the stone’s volume: it is reversible, fragile, and it changes radically what you are buying. Same trade name, different products.

Diffusion and irradiation

The diffusion drives elements from the outside into the lattice with heat: beryllium diffusion in sapphires produces attractive colours, but that colour was not born with the crystal. The irradiation uses radiation to change the hue and is common, stable and accepted, for instance in blue topaz. None of these is a moral flaw; each, however, carries a different weight on value, and must be written on the report.

Natural, synthetic, simulant

Beyond treatments there remain two categories not to be confused. A synthetic gem has the same chemistry as the natural one, but it was grown in a laboratory: true corundum, true beryl, another origin. A simulant only resembles: red glass sold as ruby, cubic zirconia as diamond, a yellow-green garnet passed off as emerald. There is nothing wrong in selling a simulant, as long as you call it by its name.