remote fuel filter bowl assembly

Glass certainly is susceptible to UV rays – in a hundred years or so it will develop a purplish tint if you're not careful.

It has also been known to sag, deform, and form ripples. After all, it's just sand that's been melted togrther.

Actually, glass is just fused silica for the most part and is a plastic medium – that is, it can be deformed by pressure.  Very old window panes are seen to be thicker at the bottom than at the top, because the glass has actually “flowed” toward the bottom under the pressure of gravity and lots of time. 

In sunlight, clear glass will develop that purplish tint after several decades due to the action of UV o the glass.  This is a faint purple – a deeper purple would be a color that was put in the glass at time of production.

I learned this long ago when I remodeled old homes in Oakland Ca. for free rent. Many of the broken windows I replaced would be 1/16-1/8″ at the top and 1/4″ at the bottom and as wavy as the curtains behind them.

That's a good question. Even tempered glass (the kind that shatters) can be bent. When I did bodywork at some shops we would use a piece of glass from a pickup truck rear sliding window to mix bondo on. After a year or so that flat glass would have a bowl in the center 1/4″ deep.

I remember learning in chemistry class that glass was a supercooled solution.  Old church window being thicker on the bottom were always used as an example of how glass flows over time.  In fact, glass is an amorphous solid that doesn't flow.  Variations in thickness of glass were a result of the manufacturing process.  The thicker end would be placed at the bottom for stability. Modern manufacturing processes result in glass with a uniform thickness.  Studies using sensitive measuring equipment show no change in thickness over time.  If there are any chemists out there please correct me if I'm wrong.

Hopefully this will put it to rest. Call me ignorant yesterday.

Hmmm…whoda thunk it?