In article ,
"Toller" wrote:

So what kinda plastic do I have? If acrylic and polycarb can be flame
finished, then I must have something different?

Did the 'fire' continue to burn, after you removed the flame? Or did it
go out after you removed the flame?

In the countertop business, acrylic material won't burn by themselves.
Polyester (which can also be completely clear) will continue to burn
after the starting flame has been removed.

The edge colour, as pointed out by another reader, can give you some
guidelines.

Acrylic, polyester, and polycarbonate all smell different too. Polyester
smells like fibreglass.

Brittleness, is not an indication of acrylic as it is les brittle than
polyester...but I do not know about polycarbonate.

Odds are that 1/4" clear plastic at a garage sale won't be polycarbonate
as it is ghastly expensive.

My bet is that you have a piece of of basic plexiglass. Plexiglas is the
same chemically as Lucite: poly(methyl methACRYLate). Polycarbonate is
Lexan. Another hint is that plexiglass is almost always 1/4".

HTH