Picture frames protect the images that are reminders of the important things in life. However, the protective glass is not impervious to accidents or acts of God. If a crack develops in a picture frame, it may be possible to repair the crack without the glass fully shattering so that the image looks like new. Repairing cracks in all kinds of glassware is similar. The important difference when working with a picture frame is to make sure to protect the picture from being damaged.
Consider replacing the glass in the picture frame rather than attempting to repair it. If the crack is major and the picture frame is of a typical size, many glass supply houses will have precut pieces of glass that can be used.
Take the picture out of the picture frame. Do this slowly and carefully to make sure that the picture is not damaged and that no shards of glass are lost.
Insert a razor blade in the crack to open it a touch wider with a rocking motion. Do not press too hard or the glass may shatter. Leave the razor blade inserted to provide space between the shards of glass for the insertion of the cement.
Heat the cement to be warm to the touch and then press the cement into the crack. Use number 200 cement for all glass. Remove the razor blade to close the gap.
Bind the edges of the crack in the glass together evenly. Removing the razor will leave a slight gap between the shards. Before the cement dries, move the glass together as closely as possible and hold it in position with tape or a C-clamp (C-clamps are tools that look like the letter C that have a screw portion that can be tightened or loosened to keep things in place). Binding the shards makes sure that they do not move out of place before the cement dries.
Dry the cement based on the instructions that came with the specific brand that is in use. Only after the cement is completely dry should the picture be reinserted into the picture frame.
Remember that you are working with broken glass. Take all precautions necessary to avoid cutting yourself. Work patiently and avoid sharp edges whenever possible.