For old windows, use a warm diluted vinegar solution to wipe away minor residue.
For old windows with a lot of grime, spray the diluted vinegar solution over the entire surface to be cleaned. Let the solution sit, and then scrub with a vegetable brush. Wipe away residue with clean water. When using this technique, remove the window from the wall and lay it flat. Diens says removing a window is easier than it sounds. Most old stained glass windows are double hung, using a rope and pulley system. Carefully remove the inside trim, which will reveal the ropes. Undo the ropes and counterweights. Locate where the rope is knotted, and insert a nail in the knot to prevent the rope from disappearing into the wall. Next, remove the window. Another alternative is to track down a window specialist through a local historical society or preservation group to do the maintenance.
To polish the glass, use a small amount of whiting spread on the window and buff with a dry vegetable brush. Whiting, also known as dolomitic limestone, comes in a powder and can be bought through regional chemical companies found online.