soft glass

Hard glass

crown glass

flint glass

glass ceramics etc

The refractive index of flint glass is 1.6, approx. This means that the speed of light in flint glass is 1/1.6 of its speed in vacuum. This makes it 187,380,000 metres per second.

If light goes from flint glass into ethanol and the angle of refraction in the ethanol is 27.6, the angle of incidence in the glass is approximately 23.21. This calculation is based on refractive index of pure flint glass being 1.60 and refractive index of ethanol being 1.361.

Flint is a common name for a form of sedimentary rock called chert, formed from microscopic siliceous (essentially quartz) skeletons of radiolarians. As such the hardness of chert is 7, which is slighly harder than glass and considerably harder than steel. If it will scratch glass it is likely to be flint. Flint is often mistaken for limestone or marble, which is much softer and will not scratch glass.

Cullet is actually a variant of word collet. This refers to the ring of glass that was left on the blow pipe when a glass blower was finished with a piece. The glass blower usually broke the leftovers off the pipe with a small hammer. The pieces were called the collets and recycled in the next batch of glass. Nowadays cullet means most any scrap glass. Flint glass usually refers to glass with a high lead content. But lead is not used much in regular glass container production anymore. Most flint glass nowadays is made with Soda and Lime (EAPG). The term flint can be applied to most any hard clean glass for recycling. Plate glass etc. Hope this helps.