If the fractures were indeed filled, presumably with an organic
substance, the burnt residue will be largely carbon which is
distressingly resistant to chemical attack. So you will need to
dissolve out the carbon and perhaps other stuff, then re-seal the
fractures. This will take serious and brutal chemistry, probably in
These steps might include immersing the ruby for several days in hot
concentrated nitric acid, then the same in hot concentrated
hydrochloric acid, checking periodically for progress. Then in hot
concentrated alkali (sodium hydroxide = lye) but I am not sure how
corundum reacts to alkalies so this would need to be researched
first. If this fails I would try molten potassium nitrate (saltpeter)
at about 500 degrees C at which temperature the potassium nitrate
will oxidize carbon, but again first researching whether the corundum
itself may react to potassium nitrate.
This is indicative only. I doubt whether you'd actually want to do
any of it. The reagents are dangerous and the outcome not assured.
But it does give you a sort of context of the steps that may be
In your specific case I'd recommend going straight to a ruby expert,
either corundum consultant Dr. John Emmett, president of Crystal
Chemistry in Brush Prairie, WA, or Richard Hughes -
Cheers & good luck!