Can a jeweler tell if a ruby has been filled or altered?

Yes, a jeweler can often determine if a ruby has been filled or altered through various methods, such as magnification or using specialized equipment. They look for signs of treatments, such as the presence of filler material in surface-reaching fractures or unusual optical effects. Additionally, advanced techniques like spectroscopy can help identify the specific alterations made to the stone. However, some treatments can be difficult to detect, especially if done skillfully.