Halozyme Therapeutics Inc (HALO)

[genisi]

Glass is another contaminant that is often observed during quality control screening. Glass particles can be generated by fracture of the vial neck or opening, from external sources such as other vials, glassware and lighting, and from delamination of the inner vial surface. Because of their density, glass particles sink rapidly to the bottom of the vial when the liquid is agitated. Glass delamination flakes are extremely thin and may be missed during visual examination. If a larger number are present, a “twinkling” effect in the solution is observed. The “twinkling” is best observed using a fiber optic light source. Delamination flakes do not sink to the bottom of the vial. Glass delamination usually occurs when a highly acidic, highly basic or sodium chloride solution is stored in the wrong type of container.

If you wanna read more (I wouldn't bother), here is the source:

http://www.modernmicroscopy.com/main.asp?article=18&print=true&pix=true