Detail of the Portrait of Johannes Uytenbogaert, 1619. Engraving by Willem Jacobz Delff, after Moreelse The Netherlands, 1580-1638

If you click on this thumbnail you will see two images side by side. The image on the left shows Delff's engraving with its elaborate text. The impression shown on the right has been cut out around the portrait (without the text) and laid down on a piece of paper about the same size as the complete engraving with text. This second sheet has also been given a false plate mark as if it were an early state of the engraving before the inscription. The plate mark was created by embossing and by adding a few touches of ink along the putative plate mark, and the blank area beneath the portrait has been given a light ink wash to resemble plate tone.

Collector's marks are very hard to yet rid of, especially in some cases when they are purposely placed so as to overlap onto the image area itself. Because there is often information carried by these marks that tells us about the earlier history of the print, these marks should not be erased.

Pencil writing on prints is quite common and very easy to remove by rubbing the area with compressed bread crumbs or with a soft eraser. If the pencil mark was made with a hard lead and an intaglio mark has been left, it may be removed by rubbing the back side of the print with a rounded object so as to "raise" the line.
Yellowed paper can be a problem, as the erased area can become white again. In this case the entire surface may have to be lightened.


Alterations due to light damage

Exposure to light causes two distinct kinds of damage: yellowing of the paper and damage to the tones.

Yellowing of paper

A certain amount of yellowing is a perfectly normal process as it is the natural oxidation of an old print. A print will not become excessively yellow if placed away from direct sunlight or if kept in a portfolio, although every once in a while, the print should get some airing. Keeping prints in portfolios requires some care too: you need to make sure that they get neither too dry nor too damp, and that they do not get too dusty.

The yellowing of paper is particularly problematic when it is irregular. This happens inevitably when the print has been framed in a poor quality mat made of ground wood pulp. The effect of the chemicals leeching out from the core of the mat board through the cut in the window mat will cause brown stains that follow the contours of the window in the mat. The effects may be more severe within the window area because this area is also exposed to light.
Furthermore, when the glass protecting the print presents irregularities such as spots or marks which cast small shadows, lighter areaas or spots will appear in those areas where light has not oxidated the paper.

	Detail of Venice, 1880. Etching by Otto Henry Bacher United States, 1856-1909
Click on this thumbnail to see the effects of mat burns and water stains on this very degraded print which was probably glued to a face mat at some time (notice the brush-like glue stains in the border). Unfortunately, part of the print was destroyed when it was removed from the mat (the print having become brittle from the poor quality mat).

The progressive yellowing of a print can be slowed down by a kind of bleaching of the sheet of paper. This is a very delicate operation which requires immersing the print in a solution. Such a "bath" is only possible if both the paper and the ink take well to it.
Such baths are usually given to engravings and lithographies printed with oil based inks and that have not been coloured with water based colours. The print must first be immersed in clean, cold water so as to wet and wash the paper. The print is then placed between two white blotting papers and a second or "bleaching" bath is given.

Bleaching is done using a variety of solutions:

1. Use a solution made of one part of water and one part of hydrogen peroxide to which a few drops of ammonia are added. Rinse the print several times with cold, clean water. The final rinsing should take about one hour. Bleach and water may be used in equal proportions but it is best to begin with a 10% solution reinforcing it a little at a time until the solution reaches 50%. However, bleaching water must be used very cautiously because it can affect the strength of the paper after some years. The great danger is that the chemical will not be entirely washed out of the paper after use. It requires hours of soaking in constantly changed water to ensure that none remains. The solution should always be very weak. Another system employs small amounts of sodium crystals. This solution is just as powerful as bleaching water but it is less dangerous. Several rinsings must follow the bleaching. This solution is made with 20g of pure sodium chloride for each liter of water to which a few drops (25 ml) of formaldehyde are added. This solution is particularly efficacious because the bleaching is done by emanation. The print is then rinsed thoroughly.
2. Another way of bleaching a print is to use 20g of chloramine T in one liter of water or 40g of sodium hypochloride in one liter of water. The latter requires a tepid neutralizing bath that contains 20g of sodium thiosulphate in one liter of water.

Local bleaching can be done by using the above mentioned solutions applied with a brush. Each spot can be dabbed with a hydrogen peroxide solution. These solutions can be also vaporized onto papers that cannot undergo total immersion. Industrial methylated spirit is particularly well suited for all types of papers that must not be dampened.

The drying that must follow these bleaching and rinsing baths should be done in a press, placing the print between two sheets of blotting paper.

Damage to the tones

Restoring damaged tones is technically complicated and a very delicate task as it requires a very light hand, good taste, and a good dose of modesty. To avoid artificial appearance, specialists should limit their work to the reconstruction of missing parts, to gluing rips, and to bleaching the paper.
Only at times, and very discreetly, should they restore a faded area with faded tones or maybe even generally brighten up the print by touching it up very slightly. However, faded colours should never be retouched. What must be sought after is a general balance of tones and lines rather than an hypothetical original state that, in any case, can hardly be recreated.



Damage due to smoke and dust

Prints that have been exposed to smoke and dust are often dirty and gray. Cleaning always begins with a dry method using compressed bread crumbs which absorb dust very well. After both sides of the paper have been cleaned, the crumbs are then brushed off.
Erasing is sometimes done with a soft eraser limiting its use to outer areas of the print, as finer lines of the print can be affected. The eraser is usually cut in such a way that small areas can be reached. Hard, abrasive erasers must be avoided or used very carefully only on certain spots and on well sized paper.
Incrustations of foreign matter can be removed by scraping with a razor blade or any other sharp instrument.

If this first cleaning is not sufficient, proceed to the wet cleaning method, making sure that the paper and inks will take well to washing. Spots can be removed or at least considerably lightened by dabbing these areas with a brush and clean water or a diluted bleaching solution. Total immersion in clean water is often practiced on engravings since they usually take well to such treatment. The print can also be washed with a very diluted chlorine solution for a few seconds and then rinsed thorouqhly in water.


Damage due to humidity

The damage done by humidity is one of the most ruinous for prints not only because it favours the growth of bacteria but also because it will make the paper buckle, dissolve the sizing, destroy the assembled pieces (glued backings, etc.) and provoke the formation of spots and water marks.

In damp conditions prints can easily become affected with mildew, a superficial coating or discoloring of paper caused by fungi. The mildew feeds chiefly on the size in the paper and by the time the discoloration produced by the dead fungus has been removed the size has practically disappeared too, leaving the paper, to all intents and purposes, as soft and absorbent as blotting-paper.
A really good, strong fibred paper will stand this, but a poor fibre relying upon the size for its strength would naturally go to pieces at once. Though the absence of size may make other papers less liable to the growth of mildew, the moisture they will contain will aid its germination. It is not uncommon for a collector to notice mildew (recently started) and to find out soon that the marks have disappeared when the print has been exposed to dry air for a short time. Sunlight and even the dryness of a living room will often check the continuance of growth, but the mildew is not dead. It is still in the paper, and will renew its activities at once if favourable conditions are restored.

To kill the spores, chemical treatment is essential. Even paper upon which there are no signs of active mildew is better treted if there is reason to suspect contamination. There is no need to place a print in formalin bath. A sponge or large brush applied to the back is all that is necessary.

If a print has undergone excessive humidity, the spots are not easy to remove. The print can be washed either partially or totally, depending on the size and amount of the spots. The spots can be treated by dabbing them slightly with a cotton tip or a brush dipped in bleaching solution.
Any wrinkling can be lessened by dampening the paper and then drying it under pressure.
Any gluing, backing up and framing should be done only after the print has dried properly.

	Detail of The Treasury Door, 1882. Etching by Charles E. Mills United States
This print has been damaged by foxing and water, which has left a stain over the affected area of the paper.

Damage due to heat

The destructive effects of heat are often closely associated to excessive dryness and to excessive humidity. When heat is very dry, paper becomes very brittle and friable and the coloured areas as well as the inks become scaly.
When heat is very damp, various kinds of plant life may begin to develop.
If the temperature rises excessively, the "burned" paper turns reddish or leaves a well known brownish border area.
Not all papers can be regenerated after suffering from excessive heat. To regain a certain suppleness, a print should be placed in damp (but not excessively damp) air. However, when paper becomes brittle, it must be reinforced by a backing-up sheet of paper.
The areas of the paper that have turned reddish should be removed being careful not to cause rips and the missing pieces should be replaced with cut outs. Only in some cases, can bleachings be undertaken.


Damage due to various types of substances

PROBLEM	WHAT TO USE
greasy spots	alcohol, benzene, talcum powder (the spots are first dusted with talcum powder and then the area is placed above a pot of boiling water. The talcum powder is then gently brushed away)
varnish or resin spots	acetone, alcohol, or toluene depending on the type of varnish that needs to be removed.
grease stains	apply "Pyridine" followed up by a careful rinsing
left over adhesive tape pieces	benzene, toluene, or hexane
rust	oxalic acid (dangerous)
wax	mineral oil
mud	soapy water or ammonia
water paint spots	cold or warm water
oil paint spots	mineral spirits or turpentine, hexane, toluene
acrylic paint spots	acetone

When a print is treated by applying solvents or substances, these should be applied with a brush making sure that the print is well soaked through. The print must then be placed below a sheet of white blotting paper.


Damage due to the hyper acidity of paper

If a paper is excessively acid it will lose its colour after a certain amount of time. It will also grow darker and will end up by destroying itself as the fibrous structure will slowly be annihilated.
The hyper acidity of paper can be measured with a pH meter or with pH papers which turn colour when put into contact with a wet surface.
This problem can easily be remedied by washing the paper and by applying some alcaline solutions.


Alterations and damage caused by biological agents

The mushrooms and bacteria that live on paper develop in a damp and hot atmosphere, especially if the prints are poorly aired or if they are kept tightly packed in groups. The softest papers are the most vulnerable ones. Biological alterations usually manifest themselves in the form of yellow spots but they may also be brown, blue, or black. At times a slight white growth can be seen on the paper surface. The parasites that cause this kind of damage can only be removed by disinfecting the paper.

	Detail of The Holy Family with Three Hares, 1498. Woodcut by Albrecht Dürer Germany, 1471-1528
The lower part of this print shows a horizontal area of loss that may be a "worm track" (as distinct from a round worm hole), or possibly the effect of silverfish damage. Silverfish are attracted to the sizing in paper, not the cellulose itself.

There are various ways of disinfecting paper:

• gas or vapour emanation carried out in a hermetically sealed box. evaporation of a liquid fungicide. Two sheets of tissue paper are impregnated with the fungicide and then put above and below the print to be disinfected.
• vaporisation of a disinfectant.

One of the most often used products for this kind of work is "Thymol" in crystal form which is applied by emanation. The damage caused by mushrooms and bacteria, as well as that caused by insects and rodents, must be corrected using the means mentioned in the previous paragraphs.



Further Reading:

The Care of Prints and Drawings (American Association for State and Local History Book Series) by Margaret Holben Ellis

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To select the professional best qualified to treat your object, contact the referral service maintained by The Foundation of the American Institute for Conservation (FAIC). They will provide you with a list of conservators in your area that can help you find an appropriate conservator or conservation treatment:

The Foundation of the American Institute for Conservation (FAIC) 1717 K Street, NW, Suite 301 Washington, D.C. 20006 Telephone (202) 452-9545 FAX (202) 452-9328 E-mail: infoaic@aol.com

http://palimpsest.stanford.edu/