Solvents, oils, siccatives, mediums, varnishes and fixatives are additives that play a critical role in the creation and life of a piece of work.
Solvents are used to dissolve the pastes, thus facilitating the use of colours.
Oils, of plant origin, act as agglomerating binders, providing strength to the stroke. Several oils are used in oil painting or emulsions. Selection of the appropriate oil is performed according to several criteria : required paste consistency, texture, yellowing in the dark, effect upon paint shades, desired drying time and mechanical strength of the film. Painters often have their own recipes involving one or more oils.
Siccatives accelerate the drying of oils, but this phenomenon must be performed in a progressive manner in order to allow drying throughout the thickness of the layer. The choice of siccative and the percentage used are crucial factors of good conservation of the pictorial layer. The colour of the siccative has no impact upon the end result.
Mediums are made from natural (Dammar gum, Mastic gum), or synthetic (acrylic) resins and oils. They provide cohesion to the work and promote drying.
Mediums may alter the consistency and appearance of the stroke by conferring a transparent, matt, satin or gloss aspect.
Varnishes may be temporary (retouching) or final for preserving the work. Varnish is selected according to the type of work, the desired effect and to drying time. It is important that a period of at least 6 months be allowed prior to applying the final varnish to the work in 2 or 3 thin layers.
Fixatives are generally resins in solution in alcohol. They are applied to oil-free materials, never to oil-containing work (with the exception of oil pastel). They promote the adherence of the stroke to the substrate and protect the work from aggression. Each fixative is designed for a specific use. Fixatives should be applied in successive thin coats.
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