The Vulnerability of Drawings
Both the support and the media used in drawing can be vulnerable. Different supports and different media are vulnerable in different ways and sometimes in ways that create tension between them. Thus their care often involves compromise.
The most common drawing supports are vellum and paper.
Vellum is extremely hygroscopic meaning that it either absorbs water from or releases water into the atmosphere as the relative humidity changes. This action causes the skin to expand and contract leading to crinkling. Media frequently used on vellum such as ink and paint are less hygroscopic and do not contract and expand so readily. As a result the media can become detached from the support and flake off.
Papers vary greatly in their fragility. Good quality paper made from linen and cotton – that is all papers made before the introduction of wood pulp in 1840 - are usually remarkably strong. However, wood pulp paper is acidic and turns brown and brittle in the light. A familiar example of this is what happens to a newspaper if left in sunlight in just a matter of weeks.
Watercolours and some inks are particularly prone to fading but different colours and different inks fade in different ways; some do not fade at all. This means that the image may not fade equally with the result that the intended colour balance is upset. The original colouring can often be found under the mount. An old drawing, that has been exposed to light for many years, may have faded to its full and be unlikely to come to further harm.
Iron-gall ink, in particular, is corrosive and may eat into the paper.
Bistre and sepia inks are not considered highly fugitive but are sometimes acidic and may therefore fade and/or corrode.
Metal-point marks tend to tarnish. Lead white, often used as heightening in renaissance drawings oxidises and turns black in the air.
Carbon and Indian inks, chalks and graphite are not usually fugitive although their durability will always be dependent on the particular recipe involved in their manufacture.
What Can be Done?
The principal factors that impact on the condition of drawings are:
- how they are handled;
- the environment in which they are kept: the light, temperature and relevant humidity;
- how they are mounted and/or framed.
Attention to these factors can greatly increase the life of a drawing in good condition.
Handling can lead to scuffs on all drawings and smudges on drawings made in unfixed media such as charcoal. Fingers can also damage drawings by depositing oil on them. Therefore drawings should be touched as little as possible. Try to hold them by their mounts rather than the support of the drawing. Some museums recommend the wearing of cotton gloves but beware as they can make you clumsier. Framing is a good option for drawings prone to smudging.
Light speeds up chemical reactions, causing some media to fade and other media and some supports to corrode. UV light is the most damaging but all wavelengths and any light causes damage. 50 Lux used to be recommended as the light level in which it was appropriate to display drawings. This led to a common misunderstanding that drawings shown at such a light level would not sustain damage. This is not true. 50 Lux was adopted on the grounds that it was the lowest light level at which, once your eyes have adapted, a drawing can be properly appreciated. In fact all light is damaging and the damage is cumulative and irreversible. This means that ideally drawings should be stored in the dark but this is not practical if the drawing is to be enjoyed day to day at home. Where you put a drawing can however make a big difference. Do avoid light from the south. It is also worth using ultraviolet filtering glass for framing which cuts out the most actively damaging light. If a drawing falls into one of the most vulnerable categories, for example has especially delicate colouring, you might consider covering it with a curtain.
Heat increases the speed of the chemical reactions that cause deterioration in paper. Paper is less hygroscopic than vellum but fluctuations in relative humidity nonetheless cause it to expand and contract giving rise to cockling and the possibility of the media flaking as occurs more often with vellum. In addition, humidity encourages both pests, leading to insect damage, and the growth of bacteria, which cause brown marks known as foxing.
Museums aim to store their drawings in a temperature between 16 -19º with a relative humidity of 45-60 %. Again, this is not practical in the domestic setting. It is probably best to aim simply to keep the temperature stable with the relative humidity no higher than 60%. Try not to hang drawings on exterior walls as they are usually more affected by external temperature changes and also not near radiators or spotlights which dry out the air.
The most important thing to remember is that drawings do not like sudden changes to their environment. If your drawings look in good condition then keep them as you have been. If they are cockled, flaking or show signs of pest damage or foxing then it is wise to seek advice from a conservator. It may be that individual micro-climates, a job for a specialist, could be appropriate for certain works, especially works on vellum.
Mounting and Framing
It is only relatively recently that the importance of appropriate mounting and framing has been appreciated. Indeed the quality of a mount or frame is one of the most effective methods with which a private person can ensure the welfare of his or her drawings.
Until recently drawings were often mounted on board made from wood pulp. You can recognise this from the brown line along the cut of a cut-mount under the mount’s facing paper. Such mount board can turn even good quality paper brown and brittle. Sometimes such mounts may have a significant role in the history of the drawing. If so they should be kept but be inter-leaved with acid-free buffering between the drawing and the mount. In most cases the mount can be replaced. Currently the best mount board available is Museum Board made of 100% cotton fibre. Conservation Board made of chemically purified wood pulp is also acceptable.
Likewise framing can cause problems if the back of the drawing is in contact with a wood or wood pulp backing board. It is also important that there is space between the front of the drawing and the glass so that the edges of the drawing are protected from the frame and the drawing can expand and contract without the medium rubbing against the glass. Again it is important to keep an old frame if it is historically connected with the drawing. If necessary, existing frames can be given additional depth and buffering material can be interleaved between the frame and the drawing to provide protection.