It is said that woodworkers basically take big pieces of wood, cut them into smaller pieces, and then glue them back together. Therefore, if you want to make fine things out of wood you need to master the art of gluing. Apply too little and your joint will fail. Apply too much and you will have a time-consuming gooey mess to clean up. After 40 years of practice, I am prepared to say that the glue lines pictured above are as close to perfection as you can get. You are actually looking at two plywood panels, each with a 1/8″ veneer glued to the edge. The veneers are placed back to back and the pair of panels are clamped together as cauls for each other. If you apply exactly the right amount of glue, distribute it evenly, and apply uniform clamping pressure you will be rewarded with the tiniest bead of squeeze-out confirming full coverage. The shims placed under the bar clamps keep them out of the glue preventing rusting of the clamps and staining of the wood.