the effective viscosity of the glass at t p such that high viscosity results in a slow rate of relaxation and a low viscosity results in a fast rate of relaxation the effective viscosity varies inversely with the fictive temperature of the glass such that a low fictive temperature results in a high viscosity and a high fictive temperature results in a comparatively low viscosity therefore the rate of relaxation at t p scales directly with the fictive temperature of the glass a process that introduces a high fictive temperature results in a comparatively high rate of relaxation when the glass is reheated at t p one means to reduce the rate of relaxation at t p is to increase the viscosity of the glass at that temperature the annealing point of a glass represents the temperature at which the glass has a viscosity of 10 13 2 poise as temperature decreases below the annealing point the viscosity of the supercooled melt increases at a fixed temperature below t g a glass with a higher annealing point has a higher viscosity than a glass with a lower annealing point therefore to increase the viscosity of a substrate glass at t p one might choose to increase its annealing point unfortunately it is generally the case that the composition changes necessary to increase the annealing point also increase viscosity at all other temperature in particular the fictive temperature of a glass made by the fusion process corresponds to a viscosity of about 10 11 10 12 poise so an increase in annealing point for a fusion compatible glass generally increases its fictive temperature as well for a given glass higher fictive temperature results in lower viscosity at temperature below t.