The basic elements of decoration considered from a structural viewpoint are the support, the ground, the 'paint' or other decorative layer, and the varnish. The relationship of these layers is shown diagrammatically in Figure 4.3. Each component in a decorative scheme has a particular function to fulfil. The desirability of properties varies with different components but adhesion to adjacent layers, internal cohesion, hardness, brittleness, strength, sensitivity to light, temperature and relative humidity, gold leaf bole •
■ varnish ■ paint gesso wood substrate
binding medium pigment particles gesso
Figure 4.3 (a) Diagrammatic representation of the layer structure of a painted and gilded surface, consisting of wood substrate and gesso ground, with paint layer/s and gilding (bole and gold leaf) covered by a varnish layer. (b) Underbound or 'lean' paint often appears matte. It has minimal binding medium that is often only barely sufficient to hold pigment in place. (c) Well-bound, medium rich or 'fat' paint usually appears glossy. The pigment particles are fully wetted by the medium h— void gesso ageing properties and overall stability are all important. The following description includes the terminology used for different parts of decorative structures, some examples of the preparations used and an explanations of the layer structure of some common types of surface decoration. For definitions of a wide range of materials used in coatings see Massey (1967).
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