All textiles have a natural tendency to decay. A prime conservation objective therefore is to minimise the impact of factors which contribute to degradation processes. A further aim of textile conservators is to preserve the integrity of an artefact so that it reflects not only its basic nature but also its history of usage. In realising this aim it may be necessary to avoid treating certain artefacts, especially if the treatment is likely to result in the loss of historical information. There will be other times however when historically significant material may have to be removed if it is considered likely to contribute to the degradation of the textile if it is retained. Each case must be judged on its merits.
As some historic textiles cannot be cleaned or softened, they will remain inflexible and therefore susceptible to fibre damage upon handling. Textile conservation is heavily based on non-interventive techniques such as using correct methods to support and handle these materials and maintaining the best possible conditions in storage and display areas. In this way, degradation processes will be slowed and significant historical and technical information will be retained.
Preventive conservation strategies are aimed at ameliorating the impacts of the main agents of textile deterioration. Some of these strategies include:
- storage and display in appropriate environmental conditions;
- control of conditions to minimise mould formation and insect activity;
- the use of appropriate storage materials, methods and handling; and
- dust control and good housekeeping practices.
Optimal temperatures and relative humidity levels for storage and display areas are 15 – 25 °C and 45 – 55 % respectively with maximum variations of 4 °C and 5 % respectively in any 24 hour period. Relative humidity levels of 70 % or greater increase the risk of mould growth, insect attack and chemical degradation of textile fibres by pollutants. On the other hand, relative humidity values of 40 % or less increase the risk of desiccation and subsequent embrittlement of fibres.
Keep conditions as stable as possible. Place artefacts in boxes, cupboards, drawers, showcases and even frames to stabilise the conditions by buffering the impact of external temperature and relative humidity changes. Keeping textiles within a display case or storage box also reduces the effects of pollution. In extreme cases seals and filters might need to be installed in the building or in the secondary containers and cabinets.
Maintain light levels where textiles are displayed at a maximum of 50 lux with UV levels as low as possible, but preferably below 30 µwatts/lumen (a total UV exposure of 1500 μW/m2). Store textiles in the dark but also ensure that light levels in storage areas are sufficient so that textiles can be examined without strain when necessary.
Regularly check display and storage areas for signs of insect activity such as the presence of insects themselves, insect cases, eggs, larvae or frass. Use and regularly monitor sticky insect traps to gauge the level of insect activity. While it is the insect larvae that do the damage, the presence of adult insects is indicative of a potential problem. Since dead insects are a food source for other insects, good housekeeping is imperative. Insects found most commonly in textile collections (carpet beetles, moths and silverfish) are best controlled by thorough and regular cleaning.
Do not eat or drink in any areas where artefacts are housed as food fragments attract potential pests.
Isolate and inspect new items for signs of infestation before bringing them into storage or display areas. This can be done by enclosing the item in a polyethylene bag for two to three weeks. Inspect the bag regularly during this period for signs of larvae, insects or frass and also to ensure that there is no relative humidity build up in the sealed bag. If no evidence of insect activity is found then the object can be registered into the collection and moved into the collection storage or display areas.
If pests are found, providing the textile is not painted, the insects in textiles can be eradicated by freezing. Although details of freezing techniques are given in an earlier chapter (see the chapter Mould and Insect Attack in Collections), it is necessary to stress the importance of wrapping the textile in tissue paper before sealing it in a plastic bag prior to freezing. The sealed plastic bag prevents desiccation of the textile during freezing and the tissue protects the textile from any condensation that might result during the thawing process.
Do not apply pesticides or other chemicals to textiles as these may be damaging to the textile and the handler.
Damage caused by mould is largely irreparable. If mould is found on a textile, isolate it immediately, place it in a lower relative humidity environment and seek the advice of a conservator. Mould can be controlled by ensuring that the relative humidity of storage and display areas is kept below 70 % with good ventilation.
Appropriate Storage Materials: Methods and Handling
Use archival quality materials in storage and display systems, particularly for those materials in direct contact with textiles. Acid-free materials (pH 7) are recommended. Some acid-free materials are buffered with an alkaline buffering agent. While these buffered materials are safe for use with plant-based textiles (cotton, linen etc) they should not be used with protein-based textiles such as wool and silk.
Where possible, individually box textile items (see later sections on storage and display). As storage in a box or framing a textile create microclimates, the best archival quality preservation materials should be used in their construction. Polypropylene or acid-free boxes are highly recommended. If brown cardboard boxes are the only storage system available, for cellulose-based textiles (cotton, linen), line the box with buffered acid-free tissue or Tyvek® and wrap the textile in buffered acid-free tissue. For protein-based textiles such as wool and silk that prefer a slightly acidic environment, line brown cardboard boxes with non-buffered acid free tissue or Tyvek®. To do this, fold the tissue paper or cut the Tyvek® to fit the dimensions of the box. Fold the tissue or Tyvek® over the artefact before putting the lid in place. Controlling the relative humidity in the store to around 50 % will reduce the extent of acid migration from the cardboard to the contents.
A well labelled storage system with easily accessible shelving is recommended. Powder coated metal shelving is preferred to wood or chipboard (Figure 3). If the latter are all that are available they must be well sealed with a water-based polyurethane lacquer or other appropriate sealant (see the section on Pollutants in Preventive Conservation: Agents of Decay).
Do not store textiles in plastic as many plastics generate electrostatic charges which attract dust. This can be easily transferred to a textile during unpacking. In addition, a drop in temperature inside the bag will increase the relative humidity and may contribute to enhanced chemical and/or biological degradation.
Examine the original storage and/or packaging of the textile as it may provide useful additional information about the ownership, manufacture or other details of an object’s history. Depending on the significance of this material, either store it separately from the textile or discard it.
Handle textiles with cotton or vinyl gloves to avoid the transfer of grease and acids from hands to the textile. Where gloves are impractical, such as when treating a textile, hands must be well washed. Do not wear jewellery whilst treating textiles as the fibres can get snagged and damaged. Support textiles when moving them, either in a box, on a roll or by spreading the weight evenly over the carrier.
Dust Control and Housekeeping
As dust can cause abrasion and discolouration and attracts moisture and insects, choose a room for textile storage or display that allows for good control of dust levels and which can be kept as dust-free as possible.
Regularly clean all shelves, floors, vents and windowsills. Use a vacuum cleaner with a HEPA filter for cleaning. Do not have carpets in these areas as they attract dust and insects.