What are hinges in stained glass?
As the glass is the strongest part of a leaded or copper foiled panel, the joining materials (lead, solder) are the places where the panel can flex. If you have long straight or nearly straight lines extending to or toward the edges of the panel (vertical, diagonal or horizontal), this is the place where the panel can completely bend (hence "hinge"). It provides a danger in handling that the panel will break. Even if the lines do not run all the way to the edge, any significantly long line will put pressure on the glass pieces at the ends of the hinges, such as a series of formal border pieces or narrow central pieces. It will be a weakness in the long term whether it survives the studio processes or not.
However, we all have seen leaded glass windows with single or multiple hinges that survive for many decades, and only as they loose support from firm cement and the ties to the saddle bars break away, does the panel begin to self destruct.
It is important to recognise where these hinges are to be able to place reinforcements on the panel.
But the real solution for making a panel that will last, it is best practice to avoid designing hinges into the finished work.