How did Corona derive at establishing the default value of IOR at 1.52?
Crown glass is a type of optical glass used in lenses and other optical components. It has relatively low refractive index (≈1.52) and low dispersion (with Abbe numbers around 60). 
Thank you for the reply. Interesting!
I am pretty sure the number 1.52 is a measurable physical property of glass/dielectrics. The “Crown” part is just a coincidence.
Or maybe…