- Age cracks
These penetrate through the ground to the paint layer and varnish. Age cracks can form different patterns depending on the paintings support, how the painting was prepared and the environment. Other types of age cracks such as sigmoid cracks, or fishbone cracks can be formed on canvas paintings through mechanical damage.
This is a cloudy bluish-white discolouration appearing in the picture varnish layer. This condition is generally considered to be the result of moisture penetrating the natural resin varnish, although other opinions exist as to the cause of its formation. Paintings exposed to damp atmosphere appear the most vulnerable. Another factor, which may contribute to the bloom condition, suggests that unsuitable materials were used in the varnish composition. Modern synthetic varnishes are much less likely to bloom than the natural varnishes.
Composition refers to animal glue based lining adhesive with a variety of possible additives such as molasses, flour and Venice turpentine, or elemi.
This is a term used to describe the process of re-attaching loose or flaking paint with adhesives by flattening the separated layers of flaking or cleavage.
Cradles were devised to prevent the warping and splitting of wooden panels. These are usually made from hard woods attached by glue to the back of a panel painting in a construction resembling latticework. A series are strips are placed at regular intervals, parallel to the panel grain. These strips are slotted to allow for a second series o strips, not attached by glue to be intersected through them.
- Drying cracks
Drying cracks or traction cracking is caused by the final varnish having been painted over partially died oil paint. The condition increases as the films slowly dry. Traction cracking is irregular in appearance, another resembling frosted tree branches. This is due to pronounced cracking in the underlying dark colours, which exposes light paint or ground beneath. Cracking seldom occurs in white pigments or paint mixed with white unless they are applied too thickly.
Another type of drying cracks is produced by the excessive use of bitumen. In the nineteenth century artist were enthusiastic over the golden glow imparted by the transparent bitumen pigment. Its use was especially prevalent in British paintings. The presence of bitumen colour is usually recognizable by the extensive separation of the paint or by the rough texture resembling alligator skin.
- Eltoline tissue
Fine, long fibred tissue paper.
In recent years conservators have replaced the term retouching with in-painting in order to emphasize that colour additions should not be allowed either intentionally or accidentally to cover the original paint.
A painting may be examined under ultra-violet light for signs indicating old retouchings. The visible eye can also see most old retouchings. Retouching mediums used in the past usually darken with age as the oil paint oxidizes, which results in the retouching appearing darker than the surrounding paint. The crack pattern will also usually extend into the retouched area and the texture can be different from the original paint.
- Keys or Wedges
Thin triangular piece of wood tapped into the corner of a stretcher: the stretcher members are forced apart, thus tightening the canvas.
Lining means the sticking of a fabric (traditionally a fine linen canvas) to the reverse side of a canvas picture. The purpose of which may be to counteract structural weakness in the original canvas itself and /or to secure cleavage between the painting ground and canvas layer.
A wooden frame over which canvas paintings are stretched. The corners are joined but not fixed. By driving keys or wedges the stretcher may be expanded and the canvas tightened.
A weave-type or binding system based on a unit of 2 warp threads and 2 weft threads.
A weave-type or binding system based on a unit of 3 or more warp threads and 3 or more weft threads. Canvas, woven in the various kinds of twill (zigzag, or chevron or herringbone, diamond), has been frequently used as paint supports by artists.