Q. Why old glass objects appear slightly milky instead of being transparent?
Like liquids, amorphous solids have a tendency to flow, though very slowly. Therefore, sometimes these are called pseudo solids or super cooled liquids. Glass panes fixed to windows or doors of old buildings are invariably found to be slightly thicker at the bottom than at the top. This is because the glass flows down very slowly and makes the bottom portion slightly thicker. The long alternate exposure of light and dark due to day and night causes heat difference which may convert amorphous to some crystalline form and this makes the appearance of glass milky.