It is suggested that the striae in glass are layers which have their origin in the same dynamic-thermal effect. A discontinuity observed in the viscosity-temperature curve seems to be consistent with a change in the flow rates of adjacent layers in the critical temperature range. Though the possibility of a formation of striae due to a lack of homogeneity cannot be excluded, it seems that the presence of striae in a chemically homogeneous glass may result from a mechanical effect, which gives rise to interlayer shear stresses. This is the reason why the presence of striae in a chemically homogeneous glass ought to be considered normal when the glass is formed into ware (ie rolling, drawing or pressing) in the temperature range where the viscosity curve which is characteristic of the glass shows a discontinuity.
