Jointing the wood panels together is a perfect job for the casein glue that I created using the milk from Harmony Organic. The reason why it is worthwhile to create a special glue for this purpose is that casein glue, once cured, is waterproof. Given the amount of water that the wood will be subjected to in applying the gesso and paint, this is an important consideration.
As you can see from the photo, the wood is being glued together using wooden splines (the thin reed that has been made to fit into the grooves of the panels). There are different reasons for this, but I use it because it makes it very simple to line up the individual panels in gluing.
What you can’t see from this photo is the bracing that has been added behind the board. Even with the precautions of careful drying and selection of the wood with special attention to its grain, some warping will happen over time (albeit with less stress if these methods are followed). In order to keep the board flat, the panel is also braced across the back of the panel with a harder wood using a dove-tailed batten. These are braces that are an elongated trapezoid which correspond to the form dug out on the back of the board. The braces cannot be glued, because the wood will continue to contract and expand throughout the seasons and would rip the board apart over time. Instead, the expansion of the board will be directed along the line of the brace.