Care and Conservation of Watercolour Paintings

By MARION MERTENS
Marion Mertens trained as a paper conservator in Canada, completing a Master of Art Conservation degree in 1985. She has worked at the National Gallery of Canada and the Northeast Document Conservation Centre before taking a position as Senior Paper Conservator at the National Library of New Zealand in Wellington in 1990. She has worked as a private paper conservator since 1997 and is currently based in Dunedin.


WATERCOLOUR PAINTINGS ON PAPER are delicate, vulnerable objects which can be easily damaged or disfigured through careless handling and inappropriate treatment. The paper conservator can often repair or remedy these problems, but as is usually true, “an ounce of prevention is worth a pound of
cure”!

The quality of the materials used plays a huge part in the longevity of an artwork. Good quality materials are more physically and chemically stable, and will therefore be more resistant to the inevitable process of deterioration. But there are other things you can do to help protect your artworks so that you can enjoy them long into the future.

Speaking specifically about watercolours on paper, there are several problems which all paper conservators regularly encounter. At the top of the list would be the damage caused by poor or inappropriate framing, followed by the adverse effects of excessive light exposure to the paper and the media.


Foxing of paper caused by poor quality cardboard backing

It has been common practice in the past for framers to glue watercolour drawings down onto cardboard backings in order to get rid of any undulation or cockling in the paper and keep the artwork flat for framing. These backings were usually a standard cardboard. Most of these contain ground wood pulp, which tends to age badly. (Newspaper is an example of a ground wood pulp product and we know how well that ages.) The cardboard will become more and more acidic over time, leading to increased discolouration and brittleness. Window mats were often glued over the edges of the artworks. These can also become acidic and cause a type of staining known as “matburn”. Most watercolour paper is of good quality and ages well, but prolonged contact with an acidic mount (backing board and window mat) can promote discolouration and staining to the artwork.


If the mount has had an adverse effect on the artwork and has no historic significance, it may be possible for the conservator to remove the backing from the artwork. Note that any inscriptions or labels should be retained. Removing an old mount may allow further treatment, such as cleaning or repair, to be carried out on the artwork. But backing removal is a very time consuming and expensive procedure, and often the damage done by the backing to the artwork cannot be undone.



Staining and discolouration of the cardboard backing
So if you are having a valued artwork framed, it is worthwhile to pay a bit extra for ‘conservation’ framing. This means that the materials used have been tested to be physically and chemically stable, and methods used to mount the work are non-invasive, reversible and will cause no harm or stress to the artwork.

The artwork should not be framed directly against the inside of the glass. In cold conditions, there is danger of condensation and mould growth occurring inside the glass. An air space between the inside of the glass and the surface of the artwork can be provided by a window mat or by a spacer built into the frame.

It is recommended that watercolour drawings be framed with UV filtering glass. This glass helps to protect the artwork by filtering out a portion of UV wavelengths in visible light. If the artwork is to be framed up to its edges, the frame opening should be slightly larger than the artwork. If the artwork fits tightly into the frame opening,
it will become distorted and cockled over time as the paper has
no room to expand during periods of higher humidity.


Acidic window mat has caused “matburn”

Artworks on paper should not be glued down. They should be attached to the backing board, either with paper hinges along the top edge or with paper corners. These methods of attachment cause no damage and are easily reversible if the work needs to be re-framed in the future.

Hanging hardware should be secure and strong enough to bear the weight of the frame.


Here are a few sites providing more detailed information about
conservation framing:



The effect of lengthy light exposure on paper and cardboard backing


Another enemy of watercolour paintings is excessive exposure to light. Light energy can initiate the chemical reactions that cause fading of media and yellowing, discolouration and embrittlement of paper. This type of damage is cumulative; it adds up over time and occurs slowly, often going unnoticed.

Some pigments (such as the earth colours) are completely stable but others are very fugitive and will readily fade on exposure to light. Blended colours may change as one of the components fades more quickly than the others. Fading of media is irreversible and there is nothing that a conservator can do to bring the colour back.

Using good quality materials will help improve the longevity of your artworks. Quality brands and high-permanence rated colours will provide some assurance of stability but it is important to avoid excessive, unnecessary or prolonged light exposure.

Light damage can be minimised by controlling the following three factors:
the wavelength, the exposure and the duration. The wavelength is determined by the type of light source used. Some light sources, such as daylight and fluorescent lighting contain a high percentage of UV light, which is the most damaging wavelength in the light spectrum. LED and tungsten light sources emit little or no UV.


Light damage. Removal of window mat reveals discolouration of paper from lengthy display.

The exposure refers to the brightness of light source. Curtains or blinds can lower light levels considerably. Light bulbs can be replaced with lower strength bulbs or dimmer switches can be
installed.

The duration refers to the length of time which the artwork is exposed to the light source. Watercolour paintings should not be on permanent display. Change them periodically. Turn the lights off when lighting is not needed. I often suggest to clients that they photograph the artworks they have on display, and then maybe once a year compare the artwork with the photograph. In this way, fading or any change in the balance of the colours can be more easily detected.

Damage can also be caused by careless handling. The surface of a watercolour drawing is easily abraded, especially the toothed surfaces of cold-pressed paper and rough paper. Even just sliding watercolour drawings over each other can cause loss of media to the ‘hills’ of the rougher papers. Drawings should be interleaved with sheets of tissue to protect the surface of each work.

It is important to provide as moderate an environment as possible.
High humidity and high temperatures can accelerate the chemical processes of deterioration. The causes for the formation of the brown spots known as ‘foxing’ are complex, but this type of staining is certainly linked with conditions of high humidity.

With care and caution, conservation treatment may never be necessary. But if you do have concerns about the condition of an artwork and would like an opinion or advice, contact a professional
conservator.


You can find us under “Find a Conservator” on the website of the New Zealand Conservators of Cultural Materials/ Pū Manaaki Kahurangi: https://nzccm.org.nz/


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