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2. Support-based elements: graphic documents

2.1 Inks: definition and composition
2.2. Deterioration and treatment of the support-based elements in manuscripts
2.3. Deterioration and treatment of support-based elements in drawings and paintings
2.4. Deterioration and treatment of support-based elements in printed documents and prints

 

2.1 Inks: definition and composition

Ink is an element based on a support by means of which signs, writing or drawings are represented; in general ink is any substance suitable for writing, printing or colouring with the use of the appropriate techniques and tools.

For an ink to fulfil its function it must have certain basic components: a colouring matter (pigments which colour the ink), a solvent (a medium in which the pigment is dissolved or dispersed), a binding agent (which holds the particles of pigment together and binds it to the support) and a mordant (a chemical substance which fixes the ink to the support and which may replace the binding agent), irrespective of whether among the components there may be other elements such as thickeners, fragrances, antiseptics, etc.

Inks which are specifically used in manuscripts are known as writing inks. The oldest of these is carbon-based ink; this is obtained by semi-combustion of organic materials which are dispersed in water and bound together by an adhesive substance although they may also contain a fixative. An ink of similar components but of poorer quality is bistre ink which is obtained by boiling soot.

Of very common use in manuscripts are metallo-acid inks which are characterized by the fact that their colour is obtained from a metal to which acid, which acts as a fixative, is added. Foremost among these inks are the ferro-gallic inks (formed by an iron salt with gallo-tannic acid), logwood inks (made by boiling the roots and branches of the Campeachy tree combined with a variety of metal salts according to the desired colour, alizarin inks (iron salt dissolved in acid, plus indigo in sulphuric acid) and vanadium inks where basically the iron of the ferro-gallic inks is replaced by this element.

Modern marker pen, ball-point and fountain pen inks are, generally speaking, aniline inks dissolved in different media. Today they are obtained synthetically from the transformation of benzene, although before the process was industrialized, they were obtained from indigo.

The inks used for printed matter are printing inks which are characterized by the use of a greasy substance as a solvent, and of pigments which are generally lamp-black or carbon-black.

Their specific features depend on the printing method in question; inks for photo-engraving are characterized by having aromatic hydrocarbons as solvents; letter-press inks used for newspapers and offset have a quick-drying agent which contributes to the rapidity of the printing process; lithographic inks contain a greasy substance (wax, fat, oils...) so that the ink will not stick to the plate, etc.

There are four major groups of coloured inks (used in drawings and pictures); inks with solid elements, water-based inks, oils and acrylic inks.

Solid colours are those which, although they might have included a solvent during the manufacturing process, at the time of application do not. They are mainly graphite pencils, coloured pencils, wax crayons, pastels, red chalks, charcoal pencils, etc.

The aqueous water-bound group uses water as a solvent. The main types of ink in this group are India ink, which has carbon as the pigment; water colours which have gum arabic as the binding agent; tempera, a medium which differs from water colours in that it has a thickener producing an opaque quality; and egg tempera which uses albumen as the adhesive agent.

Oils differ from water colours in that the pigment is dissolved in an oil, generally linseed or walnut oil.

Finally, acrylics are the most modern inks, whose main feature is that they have a synthetic binding agent which may be either an acrylic or a polyvinol substance.

2.2. Deterioration and treatment of the support-based elements in manuscripts

Of all the inks used for writing in manuscripts, those which present fewest conservation problems are inks with a carbon pigment, as carbon is a totally stable material which is not adversely affected by light or chemical agents, although there is a danger of the pigment being removed by rubbing or abrasion.

But not all inks behave in the same way. Some are prone to other alterations due to light (sepia inks, bistre, logwood, and early aniline ink...), to chemical elements which may produce colour changes (such as chlorine in sepia and logwood inks...) or to substances, such as water, which dissolve the agent which binds the pigments together.

To remedy the problems arising from exposure to light, the same advice applies as will be given for the preservation of cellulose supports; if the inks are already impaired because of this factor and they are almost impossible to read, ultraviolet radiation may be used to read them or they may be photographed using this kind of illumination, in some cases infrared and the most modern laser techniques can be used. Although applied in this case for texts which have faded due to exposure to light, these methods are also effective when fading is due to any other cause. Chemical reagents are not devoid of risks and are generally very harmful as they cause the inks to oxidize and in the long term may lead to total destruction; at the present time some are being tested with good results but they should only be applied by experts.

To avoid the problems of detachment, dissolving, dispersion or colour change of the pigment, the harmless effects of any treatment which is to be used on the writing must be verified. The solubility of the inks in any medium to be used in the restoration of the document must also be determined, as well as resistance to rubbing and the possibility of facing or changes in shade, should chemical substances such as bleaches, deacidifiers, etc. be used.

Solubility tests on the inks can be carried out in a simple way by passing - without rubbing - a cotton swab or a blotting paper impregnated with the product being tested over a small stroke in an area which is scarcely visible (preferably the lower part). Microscopic tests may also be carried out after applying a tiny amount of the product with an applicator to see whether the pigments swell or alter in any way.

In the event of alteration, the logical procedure would be to try several substitutes for the product to be used until one which does not affect the writing is found; for example, in the case of wet cleaning, if the ink is soluble in water the restorer can try alcohol and, if it is not soluble in this medium, he can substitute the one for the other.

But often there is no harmless product or the ink alters simply with rubbing. In this case we have only two alternatives: either to give up the treatment or to use a fixative which will protect the pigment on the support by covering it, thus preventing it from being affected by external agents.

Fixatives are not always the ideal solution as in some cases they are not strong enough to protect the ink, they may produce shine and changes in texture and lead to darkening (if they are not eliminated); with time they may oxidize.

They must therefore be applied in minute quantities and only where necessary. Once the restoration process is complete they should be removed and, although in some cases this last step is not possible due to the lack of adherence of the pigment, they should always be reversible so as to avoid future conservation problems.

The most frequently used fixatives are: laboratory gelatine for non-aqueous media, since it is soluble in water (it is prepared with 30 grammes per litre of water in a water bath), cellulose acetate in a variable solution of acetone, Paraloid dissolved in saltpetre, xylene or toluene and soluble nylon diluted in alcohol heated to around 35C. (See Table 4).

Any of these fixatives may be applied by impregnation, using a brush, or by spraying. The former method is more effective, as it soaks the pigment more thoroughly with the fixative, but it is not always to be recommended as in some cases the brush may smudge or remove the pigments.

Sometimes it is easier and less harmful to isolate the ink from the aqueous medium by covering the graphic elements with a thick pencil the marks of which are easily removed using an erasor.

One problem which has not yet been mentioned and which affects a certain group of inks is the acidity and oxidation specific to the metallo-acid inks, especially the ferro-gallic variety.

As already indicated, these inks are composed of an acid and a metal. The metal may oxidize and, at the same time, act as a catalyst for atmospheric sulphur dioxide which, in conjunction with the humidity present in the atmosphere, may generate sulphuric acid already present in the ink as a fixative.

In the long term, oxidation burns the support, especially where the lines are thickest. The acidity thus formed is transmitted to the remainder of the leaves in direct contact with the ink and may finally destroy the support to such a degree that the letters appear to be perforated as though stamped. This alteration is extremely serious and the only way to remedy it is through neutralization by deacidification and subsequent lamination of the support to prevent it from disintegrating.

The best laminating method from the point of view of future preservation is mechanical lamination using polyethylene since this material acts as an insulator and prevents the adjacent leaves from being contaminated by contact with the damaged text.

When the writing on a text is lost, whether due to problems with the ink or the disappearance of the support, it is better not to attempt to reconstitute it, especially if there is no document available for comparison. Touching up and reconstruction to complete missing texts must be firmly ruled out.

Only if there is a facsimile or photographic copy can the idea of reconstitution be considered; in this case it is preferable to include a copy of the information source as an appendix. Even so, there are two other possibilities: to reconstruct the writing using media and procedures differing from the original, or to make an exact copy of the lost text on a separate sheet to indicate its modern origin. If this copy is made on transparent paper it may be superimposed on the original and in this way the blank areas are filled in without any danger of falsification or documentary integrity.

2.3. Deterioration and treatment of support-based elements in drawings and paintings

The area covered by the restoration of graphic documents includes all the illustrations which complement the text as well as paintings and drawings on any support used for writing.

In contrast to manuscripts and printed documents, in painting different inks are usually applied to obtain the various colours. While some pigments are very resistant, others deteriorate easily on exposure to light (cinnabar red, vermilion, chrome yellow, prussian blue...) or to damp (emerald green...), contact-with heat (white lead...); with acid substances (lead oxide, vermilion, zinc white, cadmium and zinc yellow, alexandrian and cerulean blue, emerald and chrome green...) with alkaline substances (basic copper carbonate green, prussian blue...) or other elements such as ammonia (cochineal and alizarin crimson). Moreover, some pigments of metallic origin tend to oxidize the support or produce acidity problems similar to those which are typical of metallo-acid inks (such as verdigris, whose basis is copper acetate, used as a green pigmentation in many maps.

This indicates the risk of carrying out any treatment without first verifying the reaction of each colour; for instance, if one pigment does not change colour when the support is deacidified this does not mean that the other colours in the document will remain stable.

As already indicated, pigments are mixed with a variety of substances to obtain different types of ink. Depending on the ink, the drawing will present one type of problem or another and will require a specific restoration process.

The main problem, thus, of solid inks (pastel, charcoal pencil...) is the poor adhesion of the pigments to the support which decreases with the smoothness of the surface to which they are applied for the pigments are fixed to the support by becoming incrusted in the grainy surface of the page.

Fixation is not always the ideal solution as the pigments become amalgamated and lose their original velvety appearance. Sometimes, however, despite this effect, fixation is absolutely necessary. When this solution is inevitable, it is better to apply the fixative on the reverse side provided that the support is thin enough to absorb the adhesive. Should it prove necessary to apply the fixative on the right side it should be sprayed on, as a brush would smudge the colour.

Another danger lies in the possibility of the pigments becoming electrically charged and adhering to the glass in the frame. Correct mounting is necessary leaving a gap of 5-10 millimetres between the glass and the work. Movements which might make the pigmentation "come away" (vibration, shaking...) must be avoided, while antistatic products such as are used in photography may be applied.

The main problem with water-based colours is the solubility of the inks should the binding agent dissolve, and the possibility of cracking in the surface of the picture when the paint layer is rather thick.

Generally speaking, the permanence of water-based inks is increased the more fluidly they are applied as they then penetrate more deeply into the support fibres (watercolours). Conversely, the denser they are, the more opaque the surface layer becomes and the risk of detachment increases (tempera and egg tempera).

The problems of picture surface cracking and the solubility of the pigments may also be solved using a colour fixative; in this case it must be borne in mind that no fixative dissolved in a medium in which the binding agent is soluble should ever be used. It is recommended that the fixative be applied on the reverse side; it should be pointed out that the protective surface produced by spraying is more even but less compact than that achieved by using a brush, although brush application is safer in many cases.

The problem presented by oil paints on paper is very different from that of the other inks dealt with above. They do not normally present solubility problems in the media used in restoration and the commonest alteration is oxidation of the binding agent (oil) and deterioration of the protective varnish.

Another very common alteration is dirt adhering to these paintings which collect dust very easily due to their thick surface which sometimes presents reliefs and textures where dust can gather. The problem is easily solved by taking protective measures such as mounting the pictures under glass; in any case, paintings should be kept out of draughts.

Excessive lighting causes the yellowing of the varnishes which usually cover the oils and the oxidization of the binding agent. Moderate, indirect lighting is recommended.

Oxidation of inks with an oily binding agent is irreversible and there is no treatment for it. Layers of deteriorated varnish may be removed using a variety of solvents; the most common are ethyl or methyl alcohol, acetone and ammonia, either alone or mixed, although it is recommended that they should be diluted in a medium which will act as a neutralizer (water, turpentine or refined paraffin) in order to reduce their harmful effects. Other solvents for varnish are morpholine, dimethylformaline, amyl acetate, buytlamine, nitrocellulose solvent...

The most appropriate procedure is to carry out several tests using different products in different proportions until the most effective one which does not alter or dissolve the colours - is found. Tests should be carried out by using cotton swabs which may also be used to remove the deteriorated varnish.

Once the old varnish has been eliminated, a new coat may be applied to protect the painting against environmental aggression. It should always be transparent with a high refraction index, resistant and easily reversible in media which do not harm the work, since in the long term it will deteriorate and will have to be replaced.

The most commonly used varnishes are of natural origin, such as mastic and dammar, and are soluble in volatile solvents, turpentine and white spirit. There are also synthetic resin varnishes which are supposed to be more stable, such as polyvinyl acetate which is dissolved in ethyl alcohol. The varnish, just like the fixatives, can be applied using a brush or may be sprayed on.

Greater protection is achieved if the varnish is covered with waxes which also attenuate excessive shine. The most appropriate are microcrystalline waxes and beeswax; they are rubbed on the surface by means of a silk cloth.

The inks which present fewest conservation problems are acrylic inks as they are composed of synthetic pigments and polyvinyl or acrylic resin binding agents which alter little. Due to their high degree of stability they are the most appropriate inks for restoration work, provided that this is carried out on a part that has been inserted for, once dry, they are reversible only in warm alcohol, a process which proves to be extremely difficult.

In the case of the restoration of drawings and paintings, the criteria to be followed are slightly different from those set out in section 2.2 on manuscripts, due to the aesthetic nature of the works.

In this case they are not so strict, as loss of aesthetic harmony may imply the loss of the functional character of the work for which reason reconstruction of the graphic elements is usually advisable, provided that certain principles are adhered to:

Reconstruction should never become camouflage or 'faking' and should be recognizable at first sight. Neither should it entail unjustified interpretations of the lost areas; should there be no documentation on the area to be repaired, splashes of colour should be applied, clear-cut lines being omitted when their location is not known. The aim should be to ensure visual continuity between the margins of the original work and the lost area.

So as not to draw attention to the part inserted, no shades should be used which, either in isolation or together, clash with the original colours. The chromatic intensity of the restored area should be one third less than the original.

In the restoration of graphic elements three techniques are available:

1. Total replacement: using the same techniques as the original, provided that the same ink is not used and that the non-original nature of the restoration is obvious on the reverse side.

2. Stippling-in: reconstructing the image using stippling which, even in its chromatic shading, harmonizes with the rest of the work. It is a simple procedure which produces a good effect but it is not appropriate when the original work has been produced with this or a similar technique, unless the indications given in respect of total replacement are taken into account.

3. Hatching: this is more difficult than the above technique but the finished appearance is very good. Parallel, regular lines are drawn which, by their thickness, length and super-position, provide a finish that is clearly distinguishable from that of the original, while not detracting from the visual effect. The direction of the lines must always be vertical, regardless of the direction of the original lines, so as not to disturb the balance of the whole work

Generally, this restoration work is done using materials which are different from the original ones, unless the technique used is stippling-in or hatching.

The majority of supports do not present special difficulties except parchment which, because of its characteristics, usually repels the inks most commonly used in restoration (watercolours, tempera, Indian ink, coloured pencils...)

The possibility of preparing inks similar to the old substances is a complicated solution which must be discarded because of the doubts that might arise as to the authenticity of the whole work. Graphic elements on parchment can be restored satisfactorily using acrylic colours; one way to fix water-based colours is to apply a coat of ox-gall to the area to be treated beforehand. To make colour pencils adhere better, water-colour pencils should be used; application should be followed by dissolution in xylene or toluene, the surface being rubbed with a cotton swab impregnated with one of these solvents. Hatching with a pencil may also be used and fixed finally with a spray.

2.4. Deterioration and treatment of support-based elements in printed documents and prints

Printing inks are characterized by their high degree of stability due to the following factors:

The colouring agent, obtained by calcination of organic substances and, hence, not subject to chemical alterations due to exposure to light.

The solvent binding agent, an oil, which is insoluble in water and also in greasy substances as in the course of time it attains a certain degree of oxidation.

The problems which may arise have physical reasons or are due to the poor manufacturing process of the ink. If the oil used as a solvent was not properly decreased, it will produce a stain on the reverse side, reducing the clarity of the lines which appear silhouetted against the oil absorbed by the paper. This type of alteration is irreversible as oil, once oxidized, cannot be removed.

Conversely, when too much grease has been removed from the oil, the pigments are not properly bound together and may loosen, diminishing the intensity of the printing and producing stains on the adjacent sheets; in this case the problem may be remedied using fixatives, as explained above.

In general, printing inks used in newspapers are more liable to change due to the poor quality of their components.

Polychrome prints cause more problems than those done in black ink as the colours may be less stable on exposure to light and change when treated chemically. This is not a common occurrence, but the possibility must be borne in mind so that the appropriate precautions may be taken (solubility tests and fixation).

It frequently happens that polychrome prints were not originally so but have been coloured by hand with the use of water-based colours. In this case the precautions are the same as for watercolours.

Today the majority of colouring agents used in printing inks are synthetic and, depending on the manufacturing process, they will either be very stable or lack stability, although they generally stand up well.

A common treatment in the restoration of printed materials and prints has always been bleaching, because of the fact that these inks are usually unaffected by chlorine substances and, in the case of prints, because of the importance of the aesthetic factor. However, the detrimental effect of this process must be borne in mind as well as the need to avoid indiscriminate application and to take all due precautions; this method should be used only when aesthetic considerations require it.

The criteria for repair of printed documents are the same as for manuscripts; those given for drawings are also applicable to prints. Unlike the case of manuscripts and drawings, multiple reproduction is a characteristic feature of printed materials so there will probably be copies or documentation available with which to compare and check any missing elements.


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