On Thu, 17 Nov 2005 02:13:09 GMT, "Roger Derby"
wrote:

Terms here in the colonies are somewhat different.

Plate glass is made by flowing the molten glass onto a (preheated) iron
slab. It is the truest, flattest, available; but hasn't been made for
decades. What one gets now is "float glass" made by flowing the glass onto
a (shallow) puddle of mercury. It's almost as flat, but not optical grade.

Float glass is floated on molten tin.
Much flatter than the most part of pre-float stuff.

Brian Whatcott Altus OK