There is a new process that improves the look of rubies. Average stones with cracks and flaws are being "enhanced" by being filled with lead glass. Doctored stones are worth about 80 percent less than natural stones. There are reports that antique and vintage rings have been repaired with these less valuable rubies. In addition, most rubies have been enhanced with heat in recent years to improve color or fill cracks—a practice that has found acceptance in the market. But any process that makes a gem seem more valuable than it is should be explained to a buyer. Lead-glass-filled stones need special care. Lemon juice and other solvents make them turn white. There are laboratory tests that reveal the glass filler, so if you plan to buy or repair ruby jewelry, ask for a guarantee backed by a testing certificate.
Source: (Actual ruby) AGTA | Agta.org