The hard material is made usable by “tempering” the dry and grounded pigments with a binding water-miscible agent, usually the yolk of fresh eggs, except in illuminations, where artists used either the whites or the whole egg in the mixture. Other successful recipes include: egg yolk, egg white and poppy or linseed oil; and gum and linseed oil; casein glue and linseed oil.
It is a rudimentary process of mixing the dry pigments with water, producing a paste which is diluted with heated glue while it’s being produced, or by adding pigment to a blend, known as whiting, of finely grounded chalk and washcoat (also known as size).
This is the result of the mixture of tempera and oil, used by the first time in the 15th century. The mixture is produced by equal parts of egg yolk and linseed oil (usually), which creates a paint with similar colour effects as oil paint, with the exception of not being able to be painted thickly.
Traditionally, the technique implies a lengthy process, where the support surfaces have to be smooth, mainly stone, paper, fine set plaster planed wood, vellum and canvas.
Panels: In the preparatory process of the panel supports, usually, a sheet of linen is firstly glued to its surface and extra strips are used to mask the seams between the wood planks. Then, a mix of plaster of paris (also known as gypsum) and washcoat, which is called gesso, is traditionally applied as the base ground. After that, the first layer, which is called gesso grosso, is employed – a combination of coarse unslaked plaster and size. This conveys a to the surface a rough and porous quality, which will receive ten more layers of gesso sottile – a blend of washcoat and fine plaster previously quenched in water to delay the drying process. This lagging process conveys a bright and opaque white to the light-reflecting surface.
Large paintings: Larger tempera work’s designs are usually transferred to the paper cartoon through the method of distemper. The design was transferred to the support’s surface by “pouncing” or dabbing the outlines left by a perforating wheel on the cartoon, with a muslin bag of powdered charcoal. The intermittent traces were then corrected in the painting process.
The paint mixture was applied in large and successive brushstrokes of washes of semi-translusent colours. As it dries quickly, tempera was a very difficult technique of applying gradations, which often called for the cross-hatching technique to obtain the desired shaded modelling effect. With a plaster base, the colours of tempera were absorbed while they quickly dried, resulting in lighter hues of pastel and matte colours, which could be brightened up by a subsequent process of waxing and varnishing.
It’s the most resistant medium technique, which can withstand time, humidity and different temperatures. As it quickly dries, egg tempera creates a resistant and protective film to the support. The most unique features of this technique is the translucent overlays of colour washes and its power to become also opaque, conveying depth to the composition and intensifying the colours of its satin sheen finish. The paintings that use this technique are often marked by the crisp edges of the lines, enhancing intricate detailing and different textures, highlighting the decorative purpose of these paintings as well.
The mural painting of the Two Daughters of Amenhotep IV, discovered in the King’s House, in Egypt, from the New Kingdom and Amarna Period, is an exquisite example using tempera. In medieval times, Duccio di Buoninsegna and Giotto di Bondone marked the Byzantine style with the characteristic lack of depth of the image space and flatness of the surface, richly embellished with fields and details of gold leaf, as it is seen in Duccio’s Maestá and Giotto’s Kiss of Judas. The early 15th century Belles Heures, or Beautiful Hours, is a private devotional book, it is also the only manuscript to be entirely created by the Limbourg brothers (probably the most well-known manuscript from the middle ages), as the illuminations are marked by a luminescent colour palette. The tempera technique reached impressive heights in Sandro Botticelli’s Idealized Portrait of a Lady, where the characteristic graceful line work of Botticelli brings shapes and textures to life, and the soft gradation of the skin tones turns it into translucent flesh, enhancing the qualities of tempera. Later in Renaissance, in The Musician, Leonardo da Vinci is one of the first artists to use the technique of tempera grassa, which is most apparent in the oily effect in the vestments left by the unfinished painting of it; this technique was used here as Leonardo strove to intensify and brighten his colour palette, as well as delaying the drying time of the paint, which lend him the chance of exploring the theatricality of the chiaroscuro and the softness of his sfumato techniques. In the turn of the 19th century, William Blake developed his unique tempera mixture – thought to be pigment and carpenter’s glue – to be applied to dark copper sheets, which is used, for example, in Eve Tempted by the Serpent.
Tempera is probably the oldest technique to still be used since its creation in ancient times, to modern days.