"For the use and good and profit of anyone who wants to enter this profession."
-- Cennino Cennini, sometime before 1437
Some of these are more "unique" than "frequent", but I include them for interest.
Egg Tempera Questions
* Does egg tempera really use the yolk? Doesn't that make the paint yellow?
* Can you re-wet and re-use egg tempera paints once they have dried on the palette?
* Dry pigments are so dangerous! Does anybody sell pigments in water already?
* Can you use watercolors or gouache paints instead of pigments in water to make egg tempera?
* Can you use egg tempera painting when restoring china?
* Help! I have pinholes in my gesso and they show in the painting.
* What are the seven stages of a 14th century painting?
Yes, egg tempera uses the yolk of egg, not the white. The color of the yolk has no effect on the color of the paint, oddly enough. In fact, egg tempera is noticeably less yellow than oil paint.
No, egg temperas cannot be rewetted once they have dried. If you keep them wet too long the egg will start to spoil, and if you re-wet them, the egg can spoil, but the paint won't reconstitute.
There are some art suppliers who provide a limited selection of pigments in water, notably Sinopia. They seem to include a kind of soap to help the pigment stay wet, however, so I am concerned about whether they will last well.
I haven't used gouache or watercolors for pigments, but I know people who have and they seem to work. I would be concerned over long-term effects of the extra glues and ingredients, but for practice and playing around, it's not a bad idea..
I don't think egg tempera is suitable for restoring china. It doesn't adhere to nonabsorbent grounds, like glazed china, and it's unsuitable for any use which may get wet. There are, I understand, china paints which are a sort of low-temperature glaze. Those might be a better bet for your purposes.
I have found that a good way to deal with pinholes in the gesso, once they're already there, is to sand the panel with coarse sandpaper until it's really flat (albeit scratched), and then take a sponge or a bit of artists' canvas dipped in water and wrung out, and rub the whole panel in little circles, rewetting the sponge/cloth as needed. Then let the panel dry, sand shiny, and paint as normal.
The best way is to prevent bubbles from forming in the wet gesso mix in the first place -- the only problem is I've never completely managed it. When you make gesso, it helps to mix gently and let it sit for an hour or so before priming with it. Then, when applying it to the panel, pull the priming brush over the wet gesso a few times to pop out and smooth the tiny bubbles.
As for painting on bubble-pitted gesso, bubbles cause the most problem when you're using transparent or translucent pigments, which sit in the little pits and show up as more intense specks of the main color. Opaque colors don't have this problem. Just an observation.
I don't know what the "seven stages" of a tempera painting are. Maybe it's distilled from Cennino Cennini's "Il Libro dell'Arte" (an interesting how-to book from the early 15th century), which is available from Dover books in translation by Daniel V. Thompson.
A medieval painting starts with a wooden panel, usually poplar or pear or some other smooth, fine-grained wood. The wood is sanded smooth, then sealed with a glue made from animal skins, usually rabbit these days, but you can also use sheep- or goatskin parchment (I have done. It smells nastier than rabbit.).
The panel is primed with two grades of chalk gesso: "gesso grosso" is coarser, and lays a solid grounding for the "gesso sottile", a fine-grained, smooth surface.
The gesso is smoothed and polished, Cennini says, until it is like milk.
If there is a large area of gold on the painting, where it is to be is outlined and painted with bole, a kind of red clay which takes a high polish, mixed with animal-skin glue. The bole is polished with an agate burnisher, then ash-thin layers of gold leaf are applied with a special brush. The whole gilding thing is an art in itself.
The painting -- Cennini says -- is drawn onto the panel with a metal-point stylus, then carefully gone over with ink until there is a shaded, black-and-white underpainting.
Then the colors are carefully mixed and applied. Pigments included natural earths and clays in shades of brown, black, red, yellow, grey, and greenish; manufactured pigments such as white lead, red vermilion (mercuric sulfate -- very poisonous), bright yellow and orange orpiment and realgar (very poisonous arsenic compounds); and naturally occurring semiprecious stones painstakingly ground, such as lapis lazuli blue and malachite green. They were mixed with a little dilute yolk of egg and carefully shaded. Cennini said to be a good painting every color had to be applied three times, which is good advice even today when our pigments are so much stronger and purer.
So if I had to guess, I would say the stages of a medieval tempera painting might be: 1. Panel, 2. Glue sizing, 3. Gesso grosso, 4. Gesso sottile, 5. Gilding, 6. Underdrawing/painting, and 7. Painting. But since it's a somewhat artificial division, I can't guarantee that these are what your teacher wants.