The method of wavefront superposition in commercially prepared blanks
made from KU1 quartz glass with diameters 300-360 mm is used to determ
ine optical homogeneity. It is shown that its value, expressed as the
difference in refractive index, lies in the range 1 x 10(-5) to 3 x 10
(-5). Causes are established for the appearance of zonal and astigmati
c errors.