[IronJack]

The glass in an old window will be thicker at the bottom than at the top due to the glass’s viscosity. Granted, the difference is slight and it doesn’t manifest until many years have passed, but glass is a liquid, albeit a highly viscous one.

[imardmd1]

The glass in an old window will be thicker at the bottom than at the top due to the glass’s viscosity. Granted, the difference is slight and it doesn’t manifest until many years have passed, but glass is a liquid, albeit a highly viscous one.

And the reference for this is?

[ConfusedAndLovingIt]

Here's some information on the idea that glass is a liquid that flows over time. I understand you can't take the word of some random website as gospel, but here you go.

The 'glass is a liquid' myth has finally been destroyed