The cross in the picture is the place where four pieces of bronze meet behind glass. It is a window detail that almost no one will look at, and it is the part of the window that we spend the most time drawing.
A cross junction in a steel or bronze window is hard. The two horizontals have to thread through the verticals without losing their alignment. The drainage needs to go somewhere. The thermal break has to be continuous. And visually, the four arms should read as one piece — not as a clumsy intersection of two pieces of metal.
The way to do it is to draw the cross before drawing the window. The window is then the four panels of glass that this cross holds. It is a small reversal of how most architects think about windows, but it puts the right thing first.
The bronze here is hand-finished by a small fabricator in north London who has been making windows for forty years. We send him a full-size drawing of the cross. He sends back a sample. We argue about it. He wins, usually.
Built well, a cross junction will outlast the architects who drew it.