0.25" thick plate glass

Easily, but the idea is not to score it "deeper" it is to get a good clean score. Get the glass clean. Lay down your straight edge, a spring clamp may be needed to help hold one end, the score it just as you would any other glass.

Technique and practice are the keys here. Patience helps too.

But figuring you aren't long on either, after a good clean, even score, press no harder than double strength glass remember, put the sharpened end of a pencil, or the whole pencil if you feel up to it, DIRECTLY under the score, gently press on either side of the pencil, about 4-5 inches out, gently is the key word. Should snap right down the line.

Don't forget to allow for the cutter head to ruler distance.

Must be a really stout picture frame to handle that much 1/4" plate. Are you SURE what you have isn't tempered?

The best advice? Take your frame to a glass shop and have them cut you a sheet of "DSB" to fit. If they mess it up, they get to keep trying until they get it right.

ALSO be very aware of the weight and be careful....... If it gets away from you and breaks badly (not on the score), make sure you are out of the way. Safety glasses and gloves is probably a good idea

it is not like taking a piece single strength and just snapping it.

Also, consider using a light oil. I've watched the guy at my favorite glazier spray WD-40 (or do a quick swipe with a brush dipped in cutting oil) along the straightedge where he is going to score heavy (3/8", 1/2") glass. I haven't done this myself, but it does seem to help, and who's to argue with a guy who's probably scored a couple thousand miles more than I have over the course of his career.

It should be no trouble to get a good score and a clean break in 1/4 inch plate.

Luck -

~s