Noteworthy, there is a difference in depth between template and imprinted lens (Figure ). This difference is attributed to delayed elasticity and viscous relaxation; it can both be predicted (so that templates can be designed according to the target imprint geometry) or minimized (through tailoring processing parameters, in particular, temperature, time and normal load). In the latter case, a trade-off needs to be considered between retained porosity, and maximum intensity of processing. For the current case, we therefore fixed the imprinting temperature at 400 °C (what translates into a viscosity of 10 7.9 Pa•s, right at the limits of practical glass softening) and did not apply any additional normal load (see Figure ).