Preventive Conservation

Preventing damage to artefacts must always be the highest priority. Any treatment involves intervention, which may alter the originality of an artefact or contribute to changes within its constituents.

Preventive action does not have to be complex. Simple measures and precautions go a long way toward protecting paper objects. Some of these measures include:

• hygiene and regular, careful cleaning of storage and display areas;
• storage and display under appropriate environmental conditions;
• regular monitoring of objects;
• careful handling;
• use of archival quality materials for storage and display; and
• use of appropriate storage and display techniques.

Environment

Maintaining appropriate environmental conditions within storage and display areas will enhance the longevity of paper-based materials.

Light levels of about 50 lux, with no or very low UV content (30 to a maximum of 75 µwatts/lumen), are recommended if photochemical degradation is to be minimised (see the chapter Preventive Conservation: Agents of Decay). Do not expose paper objects to direct sunlight nor place light sources close to these items and monitor light levels carefully. Limit light exposure for paper artefacts to minimise their deterioration.

As light levels associated with photocopying are very high, indiscriminate photocopying will damage paper objects. If copying is necessary, as in the case of materials needed for study or viewing (for example, newspapers, certificates), only copy the documents once. Observe copyright restrictions and use archival quality paper for copies. Some papers may yellow, even after only one exposure. Never put original documents through the feeder of a photocopier.

Maintain relative humidity (RH) levels within the range 45 – 55 % and temperatures of 15 - 25 °C with maximum variations of 5 % and 4 °C within any 24 hour period. Information on temperature and relative humidity control has been provided earlier (see the chapter Preventive Conservation: Agents of Decay). Buildings have zones that tend toward dampness and zones in which conditions fluctuate more often. Doorways, chimneys, areas near heating and air conditioning vents and exterior walls are examples of such zones. Avoid placing valuable objects in these areas.

Should it be difficult to establish the above environmental conditions, strive to maintain conditions that are as stable as possible. Slow changes during seasonal variations should allow most objects to adjust accordingly and will minimise damage. Rapid and frequent fluctuations in relative humidity levels, in which paper objects swell and contract repeatedly, will increase the rate of deterioration. Elevated relative humidity levels will increase the risk of mould development while conditions that are too dry and hot will cause brittleness and distortion.

Handling

Paper is particularly susceptible to physical damage. Careful handling and a common-sense approach is necessary to minimise damage to paper and paper products:

• wear disposable latex (rubber) or cotton gloves when handling books, documents and paper artefacts to prevent the transfer of oils, fats and acids from the skin;
• pick up paper objects with both hands, not by one corner;
• keep fragile papers secured, covered and on a suitable support until treatment begins;
• place books flat, not upright, to prevent damage to the spine;
• unfold folded papers if the condition allows; and
• use pencils for documentation purposes since accidental marking with inks, biros, felt pens or similar may prove indelible.

Storage and Display

Hygiene and regular, careful cleaning are important to maintain paper artefacts in good condition. Guidelines for storage and display of paper artefacts include:

• keep storage areas clean, dry, well ventilated and free from insect and rodent infestation;
• regularly inspect stored material;
• do not store items in cellars and attics as they are likely to be overlooked or forgotten and these areas also tend to have greater extremes in temperature and relative humidity levels; and
• do not store collections close to food sources.

Depending on the type of paper object the following storage and display techniques and media may be appropriate:

• archival quality boxes or folders;
• cardboard boxes lined with acid-free tissue or barrier paper;
• flat storage in metal drawers;
• rolled storage on the outside of large diameter, acid-free cylinders (although flat storage is preferable);
• mounting;
• framing; and
• encapsulation.

Archival quality boxes or folders provide protection for paper artefacts. In addition to providing support, protection from dust and the danger of being squashed, boxes act as buffers to environmental fluctuations.

Do not use alkaline-buffered boards and paper for the protection of paper materials that also have leather, parchment, photographic, woollen or silk components. Use neutral, acid-free materials instead.

Although archival storage boxes, made from either acid-free paper board, polyethylene or polypropylene, are commercially available, they tend to be expensive and may not be of the desired size. A do-it-yourself box is a perfectly acceptable alternative. Acid-free boards such as foam core, archival mount and corrugated boards are all suitable and pre-gummed acid-free paper can be used for their manufacture. Storage folders can be manufactured from a variety of suitable buffered and unbuffered acid-free card (Figure 3).

Figure 3: Template diagram for a storage folder.

Should the above not be applicable, or if suitable materials are not available, store artefacts in ordinary cardboard boxes, provided these are lined with acid-free tissue, special barrier paper or archival plastic liners. The lining papers must be changed at regular intervals (every 12 months). Items in boxes are not immune from danger and should be checked regularly for insect infestation and for any changes in condition.

Flat storage, preferably in metal drawers, is recommended for items such as documents, maps, newspapers and certificates. They should be stored flat, unfolded and interleafed with acid-free tissue paper, which is slightly larger than the items themselves. Do not fold aged paper as in time the creases become tears.

Take special precautions with documents that contain attachments like seals and ribbons. Ensure these are not crushed or allowed to imprint themselves onto other documents. Place these items on top of a stack to avoid damage.

To reduce pressure on items on the bottom of a box or drawer, do not cram in too many items. Arrange items according to size so large ones are beneath smaller ones. Store objects of a similar nature, size and condition together.

If an item such as a map is too large to store flat, roll it onto either a large acid-free cylinder or a large cylinder (minimum diameter of 150mm) covered with acid-free tissue or Tyvek. Cover the entire object with acid-free tissue paper or Tyvek before rolling to prevent individual layers from pressing or rubbing against each other. Protect the outer surface of the item with a further layer of acid-free paper or Tyvek. Do not roll painted or fragile objects, or those that are thick and inflexible. Use Tyvek in preference to tissue paper as it does not tear and is easier to handle.

Framing is a useful method of storage and display as it protects paper from outside influences such as dirt and handling. To reduce the amount of damaging UV light reaching the item, use UV-absorbing acrylic in preference to glass. Unfortunately, framing is often expensive or impractical, especially for large items like maps.

Mounting (matting) provides safe support for flat paper objects such as watercolours, engravings, drawings and documents (Figure 4). When mounted, they can be handled and viewed without being touched. Use acid-free mount board, preferably 100 per cent rag mount or alkaline-buffered rag mount board for this purpose. The latter will be able to counteract acidity (present or latent) in the paper item. When choosing coloured board make sure that it is 100 per cent acid free.

Figure 4: A standard window mat support.

Use acid-free hinges or make them using bookbinders’ pre-gummed (not self-adhesive) paper tape or Japanese tissue paper and starch paste, depending on the weight and condition of the paper. Consult a conservator before attempting this.

Examples of two different types of hinging are shown below (Figure 5). The T-hinge can be used when the edges of the object are to be covered by a window mount. Since they are covered by the object itself, folded hinges allow the edges of the object to be exposed.

Figure 5: Examples of a T hinge and folded hinge. 

Never glue paper objects to their backings as many adhesives change their composition, turn yellow and may become insoluble as they age. Gluing also restricts the natural movement of paper. Hinging allows objects to move freely while they are held securely in place. Treatment of a previously rolled paper is shown below (Figures 6 a, b and c).

Figure 6: (a) Example of tightly rolled paper after being stored in a tube.
              (b) Paper unrolled after humidification and during dry cleaning.
              (c) After treatment and mounted for storage or display.

For storage and protection, cover artefacts with acid-free tissue paper. Alternatively, insert a sheet of mylar the size of the mount between the window mount and the artefact. Do not use mylar in the case of flaking paints, chalk, powdery pastels or charcoals as its electrostatic nature may dislodge pigments from the paper support. It also may burnish some surfaces. In these cases, use acid-free tissue paper instead.

A cheaper alternative to framing or mounting is encapsulation. In this technique, the paper artefact is sandwiched between two pieces of mylar or polypropylene film. Cut these pieces about 15 – 20 mm larger than the paper on all sides. Use clear, acid-free double-sided tape to join the two pieces of film on all sides apart from leaving a small uncovered length, about 20 – 25 mm (minimum), along one corner for air circulation and exchange (see Figure 7). For increased air circulation, leave one entire side un-adhered.

Figure 7: Demonstration of the encapsulation a document.

Do not encapsulate highly acidic material as the restricted air movement will accelerate deterioration. In some cases an alkaline buffered sheet can be inserted behind a document that is being encapsulated. Although this will assist in countering acidity, it has the obvious disadvantage of obscuring one side of the document.

Because of mylar’s electrostatic nature, encapsulation is not appropriate for chalk drawings, pastels, charcoals and watercolours. Materials which have attachments such as seals and ribbons are also not suitable for this method of storage. Disadvantages of encapsulation include the glossiness of mylar and its lack of UV protection.

Photographs may be encapsulated in mylar or polypropylene film. Store them upright in a box, folder or file so that they are not placed on top of each other and there is no weight pressing the encapsulating film against the photographic emulsion. Ensure that they are held in place to prevent sagging.

Tracing Paper

Tracing papers are usually translucent and have a smooth and hard surface, making them very receptive to aqueous inks. Of the variety of available tracing papers the most commonly used ones are:

• prepared tracing paper;
• parchment paper; and
• natural tracing paper.

Prepared tracing paper is manufactured from cotton pulp. The transparency of this paper is due to its impregnation with assorted gums, oils and resins.

Parchment papers (also known as pergamyn and papyrine) are produced by a process in which un-sized sheets are immersed briefly in sulphuric acid and then neutralised with ammonia. This treatment alters the cellulose structure. Sometimes glycerine or glucose is then used to coat the paper. Parchment papers are grease proof.

Natural tracing papers are produced by physically modifying the cellulose fibres. This treatment increases the surface area of the fibres without shortening them. Heat and compression treatment produce a very dense paper free of internal gaps. The surface is usually sized to make it more receptive to inks (Dobrusskin 1991).

Due to their high densities, tracing papers are very susceptible to damage caused by either exposure to high relative humidity conditions (greater than 60%) or by contact with water. These factors cause expansion, deterioration and permanent damage.

Tracing papers are among the most difficult to treat since all repairs will be obvious, due to the transparency of the paper. Any treatments must be carried out by a conservator.

Because of the difficulty of treatment, preventing damage carries even greater importance. Keep tracing papers flat and fully supported in an environment in which relative humidity and temperature fluctuations are minimised.

Books

Handling

Do not remove books from shelving by pulling the head-cap or spine. Rather, ease them out by carefully grasping them around the centre of the spine. Wear gloves when handling books.

Minimise photocopying pages of books, as the process places the spine of the book under stress. In addition, the very high light levels associated with photocopying increase photochemical degradation of the paper. If a copy needs to be obtained, taking a photograph may be a better option.

Storage and Display

Should it be desirable or necessary to display certain pages of a book, then use book cradles or blocks. These support both parts of the book, preferably on a slight angle, to avoid stress on any part of the book or spine. Keep the spine itself flat. These cradles or blocks can be bought or made using acrylic or acid-free card (Figure 8).

Figure 8: Book cradle and display.

To hold pages flat while on display, use Mylar strips, made into hoops, to ‘strap’ particular pages, including the cover. Form the loop by applying a small piece of acid-free, double-sided tape to one end of the Mylar strip. This join can be hidden underneath the book. A thin, flexible version of mylar (0.002 - 0.003 mm) is suitable for this purpose; thicker versions may damage the paper. Polyester or polypropylene films are also suitable. Turn pages regularly to avoid overexposure of any particular page.

Enclosed steel shelving is ideal for book storage. Use a curtain made from washed calico, Tyvek or similar material if enclosed shelves are not available. Store books vertically and according to their size unless they are large volumes or soft covers; store the latter flat, with minimal stacking.

Do not pack vertically-stored books too tightly, otherwise they will not be able to be removed easily by grasping around the centre of the spine. Bookends offer good support, preventing books from falling over or sagging.

To prevent the migration of acids from timber shelves, cover them with acid-free card (for example, mount board), Cell-Air or similar, cut to the width of the shelf. The card, or similar, can be replaced when dirty, worn or damaged. Treat new timber shelving with a water-based polyurethane to seal the surface.

Do not put shelving against outer walls as these areas are prone to dampness and temperature and relative humidity fluctuations.

Store pamphlets, magazines, brochures and journals in special archival folders or pamphlet boxes. These are commercially available or may be tailor-made (Figure 9).

Avoid the use of dressings on leather-bound books as their presence often complicates future conservation treatments. Always consult a conservator about the suitability of any dressing.

Figure 9: Some examples of storage boxes for paper material.

Stamps

History

The first adhesive postage stamp, the famous Penny Black, was produced in the United Kingdom in 1840. This stamp carried the head of Queen Victoria of England as its central design. The image was hand engraved, while the background was produced by a mechanical engraving process. To achieve the high detail in the printing a very smooth, good quality paper was needed. The individual corner letters in this very early example served as a precaution against forgery. Stamps were usually coated with a starch adhesive after printing. They were not perforated.

Use of the cancellation mark, to prevent the re-use of stamps, was soon introduced. Initially these marks were produced using red, water-soluble dyes (the Maltese Cross hand stamp). To minimise the opportunities for the removal of the cancellation mark and re-use of the stamps, these early dyes were replaced with carbon black printers’ ink.

Modern stamps are printed by offset lithography or photogravure techniques. Sometimes oxide pigments are added to create a holograph-like effect. The tiny pigment particles act like prisms and produce different patterns when the angle of light is changed.

Until recently stamps were usually adhered by wetting their gummed, water-soluble adhesive backings. Stamps are now usually produced with self-adhesive backings. These may cause future problems for conservators and collectors alike when the adhesive starts to break down.

Environment

Control of both relative humidity and light conditions is critical to prevent damage to stamps.

As some cancellation marks are water soluble and many of the adhesives (usually starch or gum arabic) used on stamps are hygroscopic (attract or absorb moisture), relative humidity control is important. Damage to the adhesive usually devalues the stamp. If relative humidity is not controlled, the stamp may become distorted.

Storing stamps in albums ensures that they are not overexposed to the fading influences of strong lights. If stamps are put on display, exert strict control over the level and duration of light exposure. A maximum intensity of 50 lux and 30 µwatts/lumen of UV radiation are recommended.

Storage

Although traditional stamp albums are both widely available and used, they are often not of archival quality. Plastics used to cover stamps can have serious effects. Plasticisers have the potential to act as solvents for stamp printing and writing inks.

Philatelic pages and folders manufactured to archival specifications are now commercially available. These materials provide full protection and support to the stamps without affecting the original adhesive.

Treatments

Stamp conservation treatments are extremely specialised and require the attention of a conservator.