You will need
New pane of glass
Take the window pane down from the window frame and set it on a table to work on it.
Use a heat-gun to melt the old putty from the window frame.
Scrape off the old putty with a putty knife.
Remove old glazier's points with the putty knife. Glazier's points are metal triangles used in holding the glass to the window frame.
The glass should be free from the frame, carefully take it out and discard it properly.
Use a chisel to smooth out the rough spots in the rabbet groove where the glass will be fixed. Then clean it with a damp cloth. The rabbet groove is where the glass will be inserted.
Brush a heavy coat of linseed oil on the window frame. Let the linseed oil soak around the area where the putty will be applied. Doing this ensures that the putty remains durable and pliable.
Apply a thin layer of putty on the rabbet groove to prevent draughts.
Insert the new pane of glass in the rabbet groove and press down firmly.
Fix a glazier's point on each side of the frame to secure the pane. Insert more glazier's points around the pane of glass at 10 cm (4 in) intervals. Cover the glazier’s points with putty.
Next, knead a piece of putty into the right consistency and roll it into a thin strip.
Lay the strip into one corner of the window frame.
Apply the strip of putty around the edges of the new pane of glass.
Next, use a putty knife to smooth out the putty around the windowpane.
Scrape away any excess putty.
Let the putty dry before you repaint the window.
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