"For the use and good and profit of anyone who wants to enter this profession."
-- Cennino Cennini, sometime before 1437
Sizing the Panel
(It's Not What It Sounds Like)
Coating or soaking a material -- wood, paper, or cloth --with a gluelike substance which acts as an absorption barrier is called "sizing". The glue is called "size". The traditional artist's size, which we are going to use, is rabbitskin glue, which is available from large art supply houses.
The glue takes a little time to make, a few hours to a day, but it's almost all soaking time, not you-stirring-the-cauldron time.
By the way, this and the next two steps are the classic way of preparing a panel for medieval and Renaissance painting. You can use panels prepared this way for oil paintings as well.
You will need:
- A panel of masonite or similar particle board (Older books warn about "tempered" masonite, but there does not seem to be any such thing any more.) or a well cured and dried hardwood panel, not too large.
- Dry granulated rabbitskin glue
- Distilled water (tap water will probably do, but it's better not to risk mineral contamination causing probems down the line)
- A double boiler
- Measuring cups and spoons
- Sandpaper, medium grit
- A dust mask
- A large, inexpensive priming brush
1. Mix the rabbitskin glue: Sprinkle 1 1/2 tablespoons of dry glue granules into one cup of water (If outside the US, that's about 10 grams of glue to about 250 ml water). This makes an amount suitable for a large panel or several small ones. Stir briefly, then allow to soak overnight. (In a pinch you can simply proceed, but a soak of at least a few hours makes a better glue.)
2. Sand the smooth side (or both, if they are both smooth) of the masonite until it is no longer shiny. You don't need to make it perfectly velvety, just rough. If you are using an actual wood panel, sand lightly.
3. The next day, warm up the glue mix in the double boiler until it is quite hot. Do not allow it to boil. Folks at Realgesso have determined that about 127 degrees fahrenheit (52 degrees celsius) is the optimum temperature for hot rabbitskin glue; you can measure this with a candy thermometer, if you like. Stir it smooth; this should not take long.
4. Lay the panel flat. Using the priming brush, brush the warm glue onto the panel, wetting it thoroughly but not leaving puddles. I do one side of the panel and three of the edges, then let it dry overnight and do the other side and edge. Try to dry the panel flat; second-best is nearly upright against a wall. When dry the glue may appear to have slightly crystallized on the panel; this is not a problem.
I recommend doubling or tripling this recipe and preparing several panels at one time.
The glue, if you have any left over, will cool to a rubbery gelatin. Just warm it up again when you need to use it.
But don't make more than you will use in a few days. It will go bad. Very bad.
You can also use the leftover glue to make your gesso, as detailed in the next step.
You could do more than one coat of glue, but usually one should suffice.
The next step (for which you can use leftover rabbitskin glue) is to make chalk gesso.