What is the meaning of Crown_glass?
An early type of window glass made by blowing glass into a hollow globe (crown) and then flattening it on a punty, reheating and spinning out into a flat disk by centrifugal force.
A variety of glass used in lenses and other optical components due to its low refractive index and dispersion. Originally crown glass was made from alkali-lime silicates with approximately 10% potassium oxide, but similar properties may be attained with other recipes.
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