Ever washed a glass repeatedly but never been able to get it quite as clean as when it was new. Researchers from Lehigh University have found that the problem may not be your fault. The answer could be nanoscopic cracks on the surface of the glass spoiling its transparency.
The findings, to be published by the American Ceramics Society, found that when molten glass is blown rapidly its outer surface sustains microscopic fractures when it comes into contact with air. The fractures are only nanometers in width and cannot be seen with the naked eye. When exposed to dishwashing soap the cracks etch, spread and dissolve faster than the rest of the glass. This results in the dirty look even though the glassware is clean.
The cracks are caused because as the glass is blown, the top couple of nanometers of the surface are solid but the rest is still liquid. As the material is blown and expands, the surface and interior expand at different rates resulting in cracks.