Measure the wall hole area and create the design for the glass block insert. In our case, it was three glass blocks, 8"x 8"x 4" deep, to create a 24" long rectangular insert.
Straight-cut the lumber to the measured opening, and build a frame around the glass block.
Position the glass block in the bottom channel and snug it up to the side frame piece. Install other glass blocks, inserting a spacer between each.
Attach the top of the frame using wood screws.
Secure the insert with screws or nails. Drive the screws or nails directly into the shims and along the top and bottom surfaces.
Use paintable acrylic or latex caulk to caulk around wood trim edges and wood frame gaps.
To finish, paint the trim and frame.