Measure the height and width of the glass portion in one sash of your window.
Determine how many panes you want to create per window sash. Typically, 3-by-5-foot windows have two rows of three panes per sash.
Divide the distance across your sash by the number of panes and measure that distance across the window. Make a mark on the interior surface of the window glass at the top and the bottom with the wax pencil. For a 36-inch wide window, with three panes across measure and place two marks spaced 12 inches apart. Divide the height of the sash by two, measure and mark several guide points across the window.
Use the white wax pencil marks as a guide to draw straight lines both across the window glass and up and down the glass with the white wax pencil where the faux windowpanes will be.
Cut a piece of white bandage tape 4 inches longer than the window sash. Hold the tape in your hands and spread them far enough apart to keep the piece of tape straight. Position the tape directly over, and centered on, the waxed pencil line. Press the top of the tape against the window and try your hand down the tape pressing in place. Drag the straight edge of the plastic spatula over the tape smoothing it against the window. Repeat until the panes are outlined on the glass.
Trim the excess tape away with the razor knife at the edge of the windowpane.