I’m including a section from Marilyn Stokstad’s book, Art History (page 566) on the process of panel painting. It is highly informative, and allows one to appreciate the time it took just to prep a panel for painting.
” Cennino Cennini’s il Libro dell’ Arte (The Handbook of the Crafts) a compendium of early fifteenth-Century Florentine artistic techniques includes step-by-step instructions for making panel paintings: The wood for these paintings, he specified, should be fine-grained, free of blemishes, and thoroughly seasoned by slow drying. The first step in preparing a panel for painting is to cover its surface with clean white linen strips soaked in a gesso made from gypsum, a task best done on a dry windy day. Gesso provides a ground, a surface, on which to paint. Cennini specified that at least nine layers should be applied, with a minimum of two-and-a-half days’ drying time between layers, depending on the weather. The gessoed surface should then be burnished until it resembles ivory. The artist can now sketch the composition of the work with charcoal made from burned willow twigs. At this point, advised the author, “When you have finished drawing your figure, especially if it is in a very valuable (altar-piece), so that you are counting on profit and reputation from it, leave it alone for a few days, going back to it now and then to look it over and improve it wherever it still needs something…(and bear in mind that you may copy and examine things done by other good masters: that it is no shame to you)” (cited in Thompson, page 75 ) The final version of the design should be inked in with a fine squirrel-haired brush, and the charcoal brushed off with a feather. Gold Leaf should be affixed on a humid day over a reddish clay ground called bole, the tissue-thin sheets carefully glued down with a mixture of fine powdered clay and egg white, and burnished with a gemstone or the tooth of a carnivorous animal. Punched and incised patterning should be added to the gold leaf later.
Italian painters at this time worked in a type of paint known as tempura, powdered pigments mixed most often with egg yolk, and a little water, and on occasional touch of glue. Apprentices were kept busy grinding and mixing paints according to their masters’ recipes, setting them out for more senior painters in wooden bowls or shell dishes.
Cennini specified a detailed and highly formulaic painting process. Faces, for example, were always to be done last, with flesh tones applied over two coats of a light greenish pigment and highlighted with touches of red and white. The finished painting was to be given a layer of varnish to protect it and enhance its colors. Reflecting the increasing specialization that developed in the thirteenth century. Cennini assumed that an elaborate frame would have been produced by someone else according to the painters specifications and brought fully assembled to the studio.
Cennini claimed that panel painting was a gentleman’s job, but given its laborious complexity, that was wishful thinking. The claim does, however, reflect the rising social status of painters.