tape a piece of white paper to the inside. back up about 10' and look at it from different angles. If it looks GREEN at all, it is regular glass. Low-iron or "starfire" glass will be clear from all angles without the green tint.
you can look through the end cut on a pane,if its regular glass,you cant see any farther than an 1/8" or so,with starphirre,you can see all the way to the other end of the pane.
