Craig Daniel of RealGesso quickly responded to my email and asked that we discuss the matter by phone. We talked this afternoon on the pluses and minuses of back sizing and gessoing. His board backs are neither sized nor gessoed. He mentioned that a sizing only application presents a sticky surface and that gessoing over that often leads to a twisting kind of warping, one that he described as "like a Pringle". Basically, that reverse side application is not a cure all.
Craig offered to send me a cradle to pull my panel back flush. I explained that I am only now exploring and testing--a kind offer, but not needed at this time. He mentioned that some artists work with the board cupping during mounting. Others will work only with his cradled panels. Some don't like the added depth that cradling brings. As he explained, there are different requirements for each artist.
So, where does this leave me? The warping I presented yesterday is, for me, unacceptable. I would really need to use a cradled board, or perhaps a well sized and gessoed back side. Craig's gesso work is really fantastic. He discussed how he's worked for years perfecting his recipe. It sure works for me. True Gesso offers panels gessoed on both sides so perhaps I'll give them a try. I want to check in with Natural Pigments as their boards have some back side gessoing and are quite flat although I had real trouble with their pinholes. Lastly, I could begin making my own. I plan to gain a bit of experience with that as I size and gesso the back side of some of these RealGesso boards.
What would happen with larger panels, say anything over 9x12"? Would every board without cradling warp, at least to some extent? In time, I will better know what works for me.
I poked through my library this afternoon and offer the results below. There seems to be a consensus for reverse side coating but mention of panel size is not clear. How small is "small" and how large is "large"? :-)
Luminous Brush by Altoon Sultan p. 38
"If you use large, uncradled panels, they need to be sized on both sides to prevent warping, then left to dry against a wall. Let the sized panels dry overnight."
Egg Tempera Painting by Koo Schadler
Recommends size and gesso on both sides as well as coating the edges.
The Painter's Handbook by Mark David Gottsegen
Recommends size and gesso on both sides.
New Techniques in Egg Tempera by Robert Vickney p. 40
"Step 6. Turn the panel over and repeat the process. The panel must be sized and gessoed on both sides to prevent warping."
The Artist's Handbook Version 5 by Ralph Mayer p. 315
"If gesso is applied in equal coats to both the front and back of a small Masonite panel there will be little chance of the panel's warping or twisting because of unequal tension. Some painters have prepared panels in this way, especially in the smaller sizes, and left them unbacked by wooden frames, sometimes protecting the edges with thin chromium or copper channel strips."
The Practice of Tempera Painting by Daniel V. Thompson Jr.
I could find no mention of reverse side conditioning.