From the point of view of terminology the use of the word crystal or glass is improper; instead it is correct to use the term Float.
Over 60 years ago the GLASS was "pulled" from the casting basin and preserved its imperfections.
If these defects were rectified and smoothed, thus ensuring perfect flatness of the faces and embellishing the artifact, the finished product was called CRYSTAL.
Now the use of these terms is improper because there is only one process for producing the glass/crystal and is the FLOAT: by the method of production "floating" invented by Mr Pilkington.
"Molten glass, at approximately 1000ºC, is poured continuously from a furnace onto a shallow bath of molten tin. It floats on the tin, spreads out and forms a level surface. Thickness is controlled by the speed at which solidifying glass ribbon is drawn off from the bath. After annealing (controlled cooling) the glass emerges as a 'fire' polished product with virtually parallel surfaces. (Website Pilkington)
This procedure prevents the formation of imperfections and thus it is no longer necessary to make the difference between the term glass and the term crystal when you talk of shower enclosures.