Crown glass

Crown glass is a type of optical glass. It is made without lead or iron and is used in the manufacture of lenses and other tools and equipment concerned with the visible part of the electromagnetic spectrum.

  • Crown glass is produced from alkali-lime silicates containing approximately 10% potassium oxide and is one of the earliest low dispersion glasses.
  • As well as the specific material called crown glass, there are other optical glasses with similar properties that are also called crown glasses.

https://en.wikipedia.org/wiki/Crown_glass_(optics)