Paper conservation techniques

By Bettina Ebert, Paintings Conservator and Researcher, Asiarta Foundation

Below are brief descriptions of some of the conservation treatments that may be undertaken on a work of art on paper.

Hinge, tape and adhesive removal

Hinges, tapes and adhesive remnants may have to be removed from a work of art on paper if they are adversely affecting the object. Pressure sensitive tapes usually have a rubber or acrylic-based adhesive, as well as plasticisers which may migrate into the support, eventually causing staining. As the various adhesives degrade, they become more difficult to remove. Often, deterioration of an adhesive leads to increased tackiness – the adhesive may flow into the paper fibres. Cross-linking during ageing results in discolouration which will disfigure the work of art.

Removal methods will depend on the adhesive type. 

Backing removal

If a work of art on paper has been attached to a secondary support that is adversely affecting the paper, it may be necessary to remove the backing.

Humidification, drying and flattening

Humidification of a sheet of paper may be necessary when the support is very distorted, rolled or cockled. Creases or folds in the paper may also be flattened out by means of humidification. Usually, flattening a support under pressure is not sufficient to remove distortions, as the paper fibres require realignment. This may be achieved by localised or overall humidification of the support, followed by pressing.

Washing

The process of washing a work of art on paper removes soluble deterioration products such as acids or discolouration from the support. Generally, paper that has been washed has increased folding endurance and tear strength. Washing may not be appropriate for all works on paper, since the washing process may solubilise sensitive media, dyes and pigments, or wash out fillers or sizing agents, altering the appearance of the work of art.

Stains and creases on a work of art

Wet paper is inherently fragile, and different washing approaches may be required for very brittle or damaged supports. For example, washing on a suction table or float washing may be more suitable than immersion. Water used in washing may be distilled or deionised, or may have its pH altered, depending on the desired effect. A wetting agent such as alcohol or surfactant may also be included in order to reduce the surface tension. Enzymes and chelating agents may also be incorporated.

Occasionally, bleaching may be undertaken as part of the washing process. However, bleaching is generally considered as a restoration process, as it is aimed at reducing staining or discoloration for aesthetic purposes.

Mould treatment

Mould or fungi require high moisture in order to thrive. Fungal growth on a sheet of paper will cause decomposition, although this is greatly dependent on the length of time that it has been active. While certain fungi may obtain their nutrients from cellulose, others will attack sizes and coatings or adhesives. Stains may also result from mould infestation.

Mould growth is inhibited by suitable environmental control, in particular a reduction of the relative humidity and an increase in air circulation. The mould may be removed with suitable protection only, as mould spores are a significant health hazard.

Mending

Tears in a support may be repaired by rejoining the paper with a suitable adhesive. Numerous aqueous adhesives may be suitable, depending on the type of paper. Reinforcing paper strips may be used where necessary. Occasionally, the edges of a tear may require realignment prior to mending.

Tear in a paper support

Filling losses

Losses to a paper support may be filled using inserts, pulp or by lining. Papers used for inserts should be closely matched to the original support. Paper pulp may be prepared in a blender, though a leaf casting apparatus may be more appropriate for large losses. It may be necessary to tone the fill so as to match the colour of the support.

Lining

Lining involves the attachment of the entire support to a secondary support which provides structural strength. This technique may be appropriate when the original support is heavily deteriorated and requires additional structural stability. The most common lining papers chosen are Japanese tissues, as they provide excellent strength despite being thin and flexible. The adhesives used in lining are generally the same as those used in other paper conservation treatments.

Paint losses on a watercolour

Consolidation

Friable or flaking media will require the application of some form of fixative or consolidant. Dessication or deterioration of the binding medium may be causing delamination of the paint, although the artist’s application method or choice of materials may also influence adhesion. Movement of the support may result in the formation of cracks within the paint layer, and may lead to flaking. Gouache paintings are often liable to flake, requiring consolidation.

Numerous different adhesives are available for consolidation. The choice of the adhesive depends on many different factors including compatibility, reversibility, gloss, drying time and flexibility among others. Aqueous or solvent-based systems can be opted for, depending on sensitivity of the media to moisture or other solvents.

Flaking and cracking gouache paint

The manner of application of the consolidant will have a significant effect on the subsequent appearance.

Matting and framing

Suitable storage of a work of art on paper is crucial for its long-term preservation. Using archival acid-free material as interleaf, encapsulation or matting helps reduce deterioration of a paper support from acid migration resulting from incorrectly chosen materials. Suitable housing protects a work of art during handling and transport, while isolating it from pollutants in the environment. Papers and boards used in housing will also act as buffers for the environment, reducing the impact of cyclic changes in humidity on the work of art.

Mount board chosen for matting should be of high quality alpha cellulose or rag pulp, with a neutral or alkaline pH. Hinges for attaching the paper to the mount board are usually made from Japanese paper due to its high strength and good ageing characteristics. The weight of the paper chosen for hinges must be carefully matched to the size and weight of the paper support. The weight of the hinge paper should not be heavier than the support. Attention must be paid to the grain direction of the paper fibres. The size of the hinge will depend on the size of the object. Edges of the paper are usually wet-cut to create a feathered edge, which is less likely to imprint on the support.

Overthrow mount

Usually, starch paste is chosen as adhesive, although cellulose ethers and acrylic dispersions are also used occasionally. Different types of hinge may be used, depending on the desired effect. Float-mounting is generally suitable when the edges of the work of art should remain visible. An overthrow mount is one of the most common forms of matting. In this system, the paper support is attached to the back board, while a window mount is hinged to the back board with linen tape. The mounted work of art can then be framed, or safely stored with a sheet of acid-free tissue paper as interleaf to protect the object.