| 1. The Stretcher is designed to expand by virtue of the corner joint design and the use of wedges which can be hammered in as the canvas stretches and warps over time. 2. The canvas is usually linen or flax (later cotton) which has been primed with glue, (rabbit skin or later PVA etc.) which reduces its absorbency in preparation for the primer. 3. The primer is the ground most suitable for the painting medium. Gesso was used extensively up until Victorian times having the advantage of being capable of filling the texture of the canvas for a smooth finish - lead white pigment was used later and can achieve a similar finish and is ideal for the reception of oil paint which binds well with it. More recently acrylic substitutes have been developed with the advantage of faster drying times. 4. The Painting medium and the method of application used by the artist will determine the longevity of the art work. Most techniques involve layers of pigment thinned in a variety of ways to achieve the desired effect. Artists have always experimented and often use materials which deteriorate (like bitumen) or cause reactions with other chemicals. 5. Varnish can be used as a final coat which brings all the previous layers together tonally and as a protection, or as a way of separating some layers - known as retouching varnish. Turner often used a layer of varnish to allow the application of watercolour for fine details (rigging) after which another layer would be applied, then more oil glazes before the final coat. Resin suspended in turpentine is the most common form although there are many variants. Often after the painting had reached a ripe age and accumulated surface dirt a way of "freshening up" the image would be to apply another similar varnish coat, thus most paintings of any age will have several layers of dirt trapped between varnish layers. |
