Icons are usually painted in egg tempera. To ‘temper’ a pigment or colour, is strictly speaking, simply to mix it with a vehicle substance that is a binder and dryer. Oil paint is pigment tempered with linseed oil, Watercolour is simply pigment tempered with gum Arabic.
Panel painting on gesso is traditionally tempered with egg yolk, hence ‘egg tempera’. It is an extremely long lasting and versatile medium. Once cleaned, many of the panel painting executed in this medium in the National Gallery in London have been found to be in far better condition than paintings executed hundreds of years later in oils and other media.
To prepare an egg yolk to paint with it needs to be first separated from the shell and the yolk sack. The yolk is then diluted 50/50 with distilled or purified water; many painters add a little clear alcohol too at this stage, which seems to help emulsify the fat in the egg yolk and also it acts as anti-bacterial agent and preservative, extending the time the tempera can be worked with. Iconographers tend to refer to this base mix simply as their ‘egg stock’.
To make tempera paint, the egg stock is simply mixed with a ground pigment, at first roughly equal the quantity of egg stock to dry pigment is mixed into a paste with a brush, this mixture is far too thick and sticky to be used as paint and needs to be diluted further to the individual painters preference.
There are numerous methods for working with egg tempera; some iconographers like to use the paint very dilute over a monochrome underpainting, steadily building in layers or glazes. Others use translucent optical mixes with very wet pigment applied in pure thin washes over a strong simple line drawing.
Perhaps the simplest method for a beginner to work in tempera is to use a technique called ‘Proplasmos’, Greek for ‘first skin, or ‘first layer’. In this technique all of the local colours of the composition are applied over a strong brush line drawing done in one of the darker pigments in the palette. The paint is applied in washes or glazes; the idea is to build a strong vibrating harmonious set of base colours for the composition that remain semi-transparent if possible, so that the underlying line drawing never gets completely lost. This also means that the colours will keep some of their natural ‘glow’, as light can pass through them to the brilliant white of the gessoed panel beneath.
The palette of pigments used in iconography is very important. Many of the colours used have theological and symbolic significance. For this reason, iconographers where possible and safety allows, will tend to utilise natural organic pigments.
Many of the pigments commonly used by icon painters are the natural earth colours, such as Yellow and Red Ochres and Green Earth pigments of various hues and shades, also the various darker pigments, such as the natural dark and lighter Umber and Siena Browns and Lamp Black.
Some other pigments used in iconography can be derived from quite precious and rare minerals, such as Lapis Lazuli or Azurite Blue and Malachite green.
Other traditional colours in the palette are derived from toxic substances such as Lead White and Vermillion Red. Happily Titanium Oxide has given us a perfectly usable replacement for Lead White, but equally unhappily, none of the safe red pigments available are quite as beautiful and translucent as genuine Vermillion or Cinnabar.
In the ‘Proplasmos’ method, once the base colours have been applied, the composition of the icon is re-established following the still visible brush line drawing. Then the process of highlighting the robes, features of the face, etc. can begin. Icon painters model the folds, faces and other features of the icon in a series of careful stages, getting slowly lighter with each stage until the final white, or nearly white finishing lines are reached. It is important not to ‘jump’ between tones in the modelling too quickly, subtle and gradual increments are much more effective. Sometimes, to great effect, there are dramatic uses of complimentary or even contrasting colours for modelling; for example, a particular favourite of many iconographers who use this technique, is to model over deep warm purple red with a cool blue grey.
As important as the choice of pigment is the way that the pigment is used. The first layers of the painting are loose, brushy and washy. Later as tighter modelling and highlighting is introduced, the brush marks become of paramount importance, calligraphic energetic mark making are the hallmark of the Prolasmos technique, especially in the later and finishing stages. To this end Iconographers tend to paint with high quality well-made sable or squirrel brushes, the larger squirrel brushes are particularly useful for putting on wet washes and glazes and the smaller squirrel brushes for giving precise energetic calligraphic marks for the finishing highlights.