Specialist Allegra Bettini explains the terms every buyer should know, from tack holes to foxing and craquelure
Hinging and mounting explains how a sheet of paper is attached to a secondary support, such as a mount (or mat) or backboard. If a work is ‘hinged’ at the upper corners, it can be lifted so that the sheet reverse (the back of the drawing) is visible — much like a door hinge. Works that are described as being mounted along all four edges are tacked down at each corner, meaning that they cannot be lifted from their secondary support. For some artists, this secondary support is a vital component of the artwork itself: for Paul Klee and Kurt Schwitters, for example, mounting was an important part of the artistic process.
Tack holes refer to the tiny pinpricks left on some artworks upon completion, usually at the corners of the paper, or centre edges. These are created when an artist chooses to pin a sheet of paper down during production, and provide a fascinating insight into an artist’s practice. Tack holes are not considered to have a negative effect on an artwork’s overall condition or value.
Today, the majority of secondary supports used for works on paper are acid-free. This has not always been the case, however, and many works on paper have come into contact with acidic cardboard and paper over the course of their history. Prolonged exposure can cause paper to darken or, in extreme cases, deteriorate. A skilled conservator may be able to improve affected works, depending on the severity of the damage, and the media used (ink, pencil, pastel, watercolour etc).
Long-term exposure to ultraviolet rays can damage works on paper, causing the paper itself to darken or yellow, and the media to fade. In some cases, such damage is difficult to reverse and, depending on the severity, can impact on the value of the work. Some degree of light staining is present on all works on paper of a certain age, although it can be minimised: we recommend that all of our clients have works framed behind UV-protected glass or Plexiglas to reduce exposure to light.
Foxing is used to describe a particular type of staining, which appears on a sheet as small, reddish-brown, yellow or black spots. The phenomenon is typically caused by inconsistencies in the paper’s composition. Occasionally, traces of metal are left among paper fibres during production which, when exposed to humidity, trigger a chemical reaction, resulting in these marks. Foxing is a common feature of many works on paper and, while sometimes aesthetically distracting, can often be reduced by a skilled conservator.
Certain high-quality handmade papers used by artists in the 19th and 20th centuries have a ‘deckled’ or rough edge, which would have arisen naturally during the paper-making process. Much like tack holes, this is not a detail that negatively affects condition or value — indeed, many artists preferred to work with deckled-edged sheets. Similarly, perforated edges do not pose an issue to overall condition, but are evidence that the artist was using sheets from a bound album or notebook.
Areas of a work which feature impasto (thick layers of media such as tempera, gouache or ink) can develop ‘craquelure’, visible as a network of fine cracks. Although primarily a concern for oil paintings, such cracks can appear on richly painted works on paper.