How to hang a frameless picture?

I made 2 frameless pictures using posters, a backing board and glass sandwich. I clipped them together using French clips, 2 on each side. The posters are 50w x 65h cms. I strung picture wire across the top clips and now a year later I've just noticed that in both of them the glass has cracked horizontally at... show more I made 2 frameless pictures using posters, a backing board and glass sandwich. I clipped them together using French clips, 2 on each side. The posters are 50w x 65h cms. I strung picture wire across the top clips and now a year later I've just noticed that in both of them the glass has cracked horizontally at the height of the top clips. I can't use D-rings as the backing board is only 3mm. The glass is also 3mm and the clips were for up to 7mm. Does anybody have any ideas as to why this has happened? Maybe I should have used more clips?
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