An Expose' on Flux

I always wanted a pair of real ruby slippers; I think most young girls having watched “The Wizard of Oz” do.  However, with my recent knowledge on the ruby market; I’m not so sure.  Apparently there are some fundamental misunderstandings when it comes to flux in Rubies.  You see we have been led to believe that flux was an unavoidable “residue” left over from the heating process and that borax was used to protect the stone from the heat.

Dr. John Emmett, President of Crystal Chemistry in Brush Prairie, Washington says that the flux which is present in some processed rubies is NOT a “residue”; but rather an infiltration that is fundamental to the processing.  In fact it is as fundamental as impregnating emeralds with oils or plastics to REDUCE THE VISIBILITY OF FRACTURES.

In laymen’s terms; borax is to a ruby what oil is to an emerald: make up.  It is solely for the purpose of hiding fractures and imperfections.  You see Borax (AKA: Sodium Tetraborite Decahydrate) starts to decompose by losing water at 80 degrees Celsius and the anhydrous material melts at 741 degrees Celsius.  This means that its melting point is well below the heat temperature for treating gems which is 1600-1759 degrees Celsius.  Therefore it could not by any stretch of the imagination protect the stone from the heat. 

In fact, you can drop natural corundum out of a furnace and into a bucket of water with out cracking it.  Apparently every heat treater knows this, it’s common knowledge among those whom are in the business of heat treating gems. 

To avoid getting too far down the rabbit hole of chemistry here, I’m gonna break it down.  Some Rubies contain deposits of Aluminum Hydroxide, which when heated turns into Aluminum Oxide.  Aluminum Oxide is amorphous and scatters light poorly (not so shiny L) it also leaves fissures or cracks in the stone.  In comes molten Borax, which wicks into the fissures dissolving the Aluminum Oxide.  These two components combined create Alumino-Borate compounds.  These compounds have high indicies of refraction and thereby do a fair job of matching the corundum; just as oils do for emeralds.

This is all fine and well when one knows they are buying a ruby with fissures that have been patched; rather than a ruby with natural “residue” from the heat treatment.  Gemologists now understand this misrepresentation, but the industry has called these fissure repairs “residue” for so long and has increased acceptance of the material, so the term remains.