Step 2: Carefully remove the putty

Picture of Carefully remove the putty
Go around the window with the razor blade inserting the blade between the wood and the glazing putty.  If the putty is old it should be cracking away from the wood and can be picked or snapped off.

The two things that you need to look for are
  1. Glazer points
  2. small bumps of putty stuck to the wood
Try to locate the points there should be at least one per side but there could be as many as three or more.  See picture for the different types of points you my find.  

Cut down.  Take your time make several passes don't rush don't push against the glass.  Make sure their are no bumps of putty that will hold in the glass.  There should be a knife thick grove between the window and the wood.  Watch out for points dulling the razor. 

When i have broken the pains it was because of these bumps or hidden points.