- Gently remove the cement from under the came leaves. You can use most any kind of stiff blade. You don't have to get it all out at once. Just work round the whole piece of glass.
- With a sharp lead knife, cut diagonally into the solder joint until you are half way through.
- With a stiff blade gradually work the leaf of the came upwards. A stiff oyster-type knife (properly called a stopping knife) works really well.
- Continue to gently lift the leaves of the came until they stand vertical almost back to the heart. This obviously is much easier on thicker came than thinner. I will not try to do any less than 6mm, and that is difficult. It is also more difficult to do with half round came than with flat came.
- With grozing pliers gently lift the solder joints. Be careful of the surrounding glass, so that you don't have to replace more glass.
- If you haven't already now is the time to tape the broken glass together.
- Work out the cement between the came and the glass. This should provide you enough space to work the glass out.
- In some cases the glass won't come out in one - taped together - piece. Now is the time to take a rubbing of the opening so you know exactly where the leaves of the lead came are. It provides a pattern piece.
Smash the glass out. Wear safety glasses and gloves.
- If the glass has come out in one taped piece, use it as a pattern. You can trace round it with a felt tip pen and cut inside the lines. You can put it under the new glass and cut, using the edges as the cutting lines. You can also make a paper pattern from the glass.
- Insert the replacement glass into the opening. Most likely it will not fit in some places. See if the lead came leaves can be opened a little more. Also mark where the glass is too large. You can groze the glass, or if you are near a grinder, grind off the "high" spot.
- Now that the glass is in the opening, begin to gently smooth the came leaves toward the glass with your stopping/oyster knife. Start by only gently changing the angle of the leaf. Any large movement of the leaf will greatly deform it.
- If the solder joints are still standing up, take your stopping knife and gently tap the end of it with a hammer. The stopping knife should be parallel to the glass. Any hard hitting will tear the solder joint from the lead. (If you were doing this on a bench rather than on a vertical window, you could heat the solder joint and re-solder without all the tapping.)
- Push stiff cement coloured black under the leaves of the came from both sides if possible. Clean off excess. Polish with a soft brush.
If there are lots of broken pieces next to each other, repair one at a time, as each piece of glass supports the other. Alternatively, take the whole panel/window out and do it on the bench.