First, clean the emerald thoroughly. Warm conditions help the cleaning process. If you warm both the stone and the cleaning liquid or filler together, you’ll open the stone’s pores, which will allow deeper penetration.
Don’t boil the emerald or immerse it in hot liquid. You’ll crack or shatter the stone.
A simple overnight soak in a jar of the cleaning medium on a hot plate may be enough to clean the emerald. (Again, warm conditions, not hot).
First, try organic solvents. Organic solvents safe for use with emeralds include the following:
- Methyl alcohol
- Ethyl alcohol
- A methylene chloride solution for dissolving cured epoxy and polyester resins
These preparations can evaporate in air and leave a residue worse than the original problem. Therefore, use a covered container.
If the organic solvents don’t remove the contaminants, you can use acids. For an intense cleaning, try aqua regia, a mixture of one part nitric acid to three parts hydrochloric acid.
Please note: hydrochloric acid fumes are toxic. Just the slightest whiff will burn your nose.
If your emerald has orange or brown rust stains, you can remove them with a solution of oxalic acid.