During the second half of 15th century many artists experimented with drying oils (nut, poppy, linseed) either in form of an additive to egg emulsion (what is usually called tempera grassa, “fat” tempera) or in combination with tempera (painting with oils on top of an underpainting with tempera or tempera grassa ).
From Egg to Tempera Grassa to Oil
Evolution of painting medium during the Renaissance
One of the characteristic aspects of the Renaissance is the gradual transition from pure egg tempera painting on panel toward oil painting on canvas.
It is not true that oil painting was discovered during the Renaissance, Medieval and Renaissance artists knew about oil medium and used it for specific tasks (painting on metals, wood, glass etc., see Theophilus). Cennini speaks about using oil even for painting on walls, and recent restoration reports confirm Giotto used some kind of tempera grassa (casein or egg tempera with additions of oil) to paint in secco [on dry plaster] in the Scrovegni Chapel. Cennini speaks also about painting with oil on panel to achieve transparency and isolate problematic pigments such as copper green (verdigris):
HOW TO PAINT WATER
Whenever you want to do a stream, a river, or any body of water you please, either with fish or without, on wall or on panel; on a wall, take that same verdaccio which you used for shading the faces on the mortar; do the fish, shading with this verdaccio the shadows always on their backs; bearing in mind that fish, and in general all irrational animals, ought to have the dark part on top and the light underneath. Then when you have shaded with verdaccio, put on lights underneath, with lime white on the wall; and with white lead on panel. And make a few shadows over the fish, and all over the background, with the same verdaccio. And if you care to make any outstanding fish, lace it with a few spines of gold.
Then, in secco, lay verdigris in oil uniformly over the whole ground; and work this way also on panel. And if you do not want to work in oil, take some terre-verte, or malachite, and cover evenly all over; but not so much that the fish and waves of water do not still show through; and, if they need it, put a few lights on the waves, with lime white on the wall, and tempered white lead on panel.The craftsman’s handbook by Cennini, Cennino, active 15th century; translated by Thompson, Daniel Varney, 1902- ed
But, in fact, the fashion of using oil on panel in addition or instead of egg tempera came from15th century Flanders, first Jan van Eyck (1390-1441), later Hans Memling (1430-1494), Hugo van der Goes (1440-1482) and others achieved outstanding results and extraordinary optical effects with oil painting on panel. Their paintings and painting techniques traveled across the Alps and influenced many Italian artists. Antonello da Messina (1430-1479), to whom Vasari attributes the “import” of oil painting in Italy was probably one of the first Italians to employ this medium fully in his works.
During this long period of transition, tempera grassa was one of the most common mediums and many artsists including Giovanni Bellini, Sandro Botticelli, Piero della Francesca and others used it to blend their brush strokes, achieve smoother transitions of colors and increased transparency of glazing.
Giovanni Bellini has started his artistic career in the middle of 15th century working with pure egg tempera in his early works. Llike many other Quattrocento Italian painters he has started experimenting with oil mediums and gradually transited to working with pure oil in his last paintings. His entire career is a testimony to this research, most of Bellini’s works were executed with a combination of egg and oil: either in form of tempera grassa or as separate layers (underpainting with tempera finished with oil glazes).
The difference between pure egg tempera and tempera grassa will be evident if you compare the difference between the brushstrokes in these two paintings by Giovanni Bellini:
Making Tempera Grassa
Materials & Tools
We do not know exactly what recipes did Quattrocento artists employ to make tempera grassa. We have a very little written documentation and technical investigation of the panels can only show us the presence of protein (egg in most cases) or oil in the binding mediums, but not their kind or exact amount in the recipe. In addition to that, artists were most likely using “leaner” or “fater” emulsions for different occasions (parts or layers of the same painting could be painted with less or more oily medium).
Therefore, this section will mostly rely on discoveries and experiments of 19th and 20th century artists and some basic understanding of chemical composition of the egg.
The chemical composition of egg
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The amount of Lecithin (an amphiphilic molecules, that attract both water and fatty substances allowing water and oil emulsification) in egg yolk allows addition of oily substances to it of about same volume as the yolk itself, without loosing the solubility of the emulsion in water. Therefore, most recipes combine 1 part of yolk to 1 part of oily medium (a mix of different types of drying oils and resins).
Let’s do some Alchemy!
Basic egg tempera ingredients
Since the very early days of our civilization eggs are used in a variety of fields. In art, each part of the egg has its particular uses:
- Egg yolk is mainly used as binder to work on panels and to make emulsions
- Egg white (also know as glair) is used as binder to paint on parchment and paper, it creates a very hard and shiny veil and thus sometimes white of the egg was used as varnish
- Egg shells, rich with calcium, were also powdered and used as an additive to colors or even as pure pigment.
A drying oil is an oil that hardens to a tough, solid film after a period of exposure to air, at room temperature through a chemical process called polymerization. This process is not reversible, i.e. fully polymerized drying oil can not be dissolved (on the contrary of resins, such as damar, copal etc. that remain re-dissoluble forever.)
There are many types of oils used by artists:
- Linseed oil
- Walnut oil
- Poppyseed oil
- Safflower oil
Oils can be prepared in different forms:
- Cold pressed
- Sun thikened
Each has different qualities (viscosity, drying time, color etc.)
Natural resins (Dammar, Mastic, Amber, Copal etc.) are most commonly known as main components of a final varnish, but they were also widely used as additives to oil and tempera grassa to change brillance, hardness, visocity and other properties of the paint.
When used alone, without egg or oil, they remain re-dissoluble, don’t yellow with time and therefore are widely used by restorers as a reversible medium.
Clean water, typically rain or spring water was used. We will use distilled water.
The recipes of tempera grassa are infinite. Egg’s emulsifying properties make it possible to mix it with all usual additives of oil and water based mediums.
- White wine vinegar (or white wine, or other types of vinegar) was used as a preservative in recipes including organic ingredients, such as egg, hide glue, oak galls and other ingredients of plant and animal origin.
- Egg white: adding whipped egg white will make the paint film glossier and harder
- Fig sap: in Italian called latte di fico, “milk of fig tree” appears in recipes including the whole egg (youlk and white together) presumably it blended the white and yolk together, and reduced any tendency to brittleness which might have resulted from the use of so large a proportion of egg-white in the medium.
- Gum arabic can effect adhesive properties and viscosity of the medium
- Ox Gall: improves the flow of egg tempera and watercolor paint, helps egg tempera adhere to gold and other metallic foils
How the yolk should be emulsified:
The yolk is emulsified with the oil of lavender by the mayonnaise system, one drop of oil at a time rubbed in thoroughly with the muller on the slab. The egg should become somewhat paler and thicker. It is put in a jar, covered with a damp cloth, and a portion of it returned to the slab, where the linseed oil is worked into it in the same way with the muller. After four drops have been emulsified, more egg mixture is worked in, and the procedure is repeated, the oil being added in gradually increasing amounts after each addition of egg. When it is finished the emulsion should be stiff ”mayonnaise.” The two volumes of water are apparently to be added at the end, small portions at a time.The artist’s handbook of materials and techniques, by Mayer, Ralph, 1895-1979, Faber, London
Pietro Annigoni’s Tempera Recipe
Recipes from Ralph Mayer, The artist’s handbook
Source: The artist’s handbook of materials and techniques, by Mayer, Ralph, 1895-1979, Faber, London