Glass surface iridescence

Observation of the nature of the corrosion products on buried glass goes back at least as far as Brewster (1863), who reported the characteristic flakiness and surface iridescence. Under the microscope he observed a fine laminar structure with a range of thicknesses between 0.3 and 15 pm, which he deduced... 

Figure 7 Fragment of an archaeological vessel glass damaged by iridescence a network of micro-cracks is covering the entire surface, which has already partly flaked off...

Figure 17. Roman glass that suffered a leaching process. Iridescence is caused by the silica layers on its surface...

A third system that is claimed to behave as a model hard sphere fluid is a dispersion of colloidal silica spheres sterically stabilized by stearyl chains g ted onto the surface and dispersed in cyclohexane ". Experimental studies of both the equilibrium thermodynamic and structural properties (osmotic compressibility and structure factor) as well as the dynamic properties (sedimentation, diffusion and viscosity) established that this system can indeed be described in very good approximation as a hard sphere colloidal dispersion (for a review of these experiments and their interpretation in terms of a hard sphere model see Ref. 4). De Kruif et al. 5 observed that in these lyophilic silica dispersions at volume fractions above 0.5 a transition to an ordered structure occurs. The transition from an initially glass like sediment to the iridescent (ordered) state appears only after weeks or months. 

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