I have had the question above asked. It seems appropriate to respond as part of the tips section, as I had made unwarranted assumptions in posting the waxing up recipe.
Waxing up is the process whereby the cut and sometimes partially painted glass pieces are assembled on and stuck to a glass sheet - called a glass easel - before raising it to a window to get the light that it will receive when installed. This allows you to see what the current state of the window is and how it would look when installed. It shows up weak areas, or pieces which are not really compatible. Although it is used mainly by those who do a lot of painting on their glass, it is equally valuable to assess the composition of a leaded or copper foiled piece. It does ensure that you do not get surprises when you have finished a piece.
The wax used is sticky and stiff enough to hold the glass, but not so sticky as to be difficult to get the pieces off the glass or the wax off the pieces of glass being prepared.
Also some users of the glass easel method paint representations of the lead lines on the back side of the supporting glass to ensure the values of the lines are appropriate for the amount of detail for the various areas of the panel.