soda–lime glass undergoes a steady increase in viscosity with decreasing temperature, permitting operations of steadily increasing precision. the glass is readily formable into objects when it has a viscosity of 10 poises, typically reached at a temperature around 900 °c. the glass is softened and undergoes steady deformation when viscosity is less than 10 poises, near 700 °c. though apparently hardened, soda–lime glass can nonetheless be annealed to remove internal stresses with about 15 minutes at 10 poises, near 500 °c. the relationship between viscosity and temperature is largely logarithmic, with an arrhenius equation strongly dependent on the composition of the glass, but the activation energy increases at higher temperatures.