More on Gesso. Addenda 4-13-13
Gesso tools, microwave, rubber bowl for mixing in the whiting, etc., jar of gesso, salt, a battered brush and a knife for mixing.
My colleague on the Picture Frame Labels blog, Framewright Richard Christie has a recent post about applying a size coat before gesso. Previously, here, I've talked about my approach to gesso, and though Richards method is traditional, I think my method works as well. My gesso is thin, or light on the ratio of whiting to glue mix, as I will spray the final coats. When I brush on what is essentially a size coat, I really work the gesso mix into the wood, scrubbing it in and when the brush starts to drag, I will add more liquid to keep it working, finally "licking" it all out. The idea is to have an even, thin coat. Because I work it, there is ample penetration; with the whiting in the mix I can see where the coating is heavy or light. There are, I believe some recipes that call for different glue to water ratios for the size coats and the actual gesso; I don't believe that is necessary.
Richards method adds a second size coat. My feeling is that coat will not penetrate or soak into the wood more than the first, as the wood has already taken up the moisture from the first coat, and dried. The second coat would need to liquify the previous coat to penetrate more. Just my feeling, though.
Another variation; Richard fills imperfections first. I usually leave that step to after the gesso is applied and dry. Then I fill, where I can readily see the problems, using either a putty made from the gesso mix, (liquid gesso, with more whiting added to make a putty) or sometimes just commercial spackle. The imperfections are primed, and the materials are compatible, though I doubt wood filler used on the bare wood is a problem. Just a different approach.
As to which method is best, or a more sound practice, is probably not easily answerable, with out a healthy addition of time. The advantages for me, of readily seeing the quality of the first coat; with the working and licking off, out weigh any advantages, perceived or otherwise, of the traditional approach, and what may be a slightly sounder method.
Addendum: I started spraying gesso after noticing the signs on some antique frames. I had the equipment, but I had never read about spraying gesso, but I went ahead. It does appear to be fairly common, though. Another method is what appears to be moldings that have been dipped in a tank of gesso. They have a very thick gesso, that covers the whole molding. It's pretty easy to work out a methodology for doing so, either as stick molding or even completed frames. Stick would probably be easier and more efficient, and I'm sure a similar method was used for the heavy antique frames using cast plaster ornamentation.