Textiles and the Environment – Canadian Conservation Institute (CCI) Notes 13/1
CCI Note 13/1 is part of CCI Notes Series 13 (Textiles and Fibres)
Textiles are among the most sensitive objects in museum collections due to their organic nature. Their long-term preservation is affected by numerous agents of deterioration, including light, incorrect relative humidity (RH), incorrect temperature, pests, physical forces and pollutants. General guidelines on these issues for all collections, including textiles, can be found on the Canadian Conservation Institute (CCI) website under Caring For: Collections - 10 Agents of Deterioration and Environmental Guidelines for Museums - Temperature and Relative Humidity.
This Note presents ideals towards which an institution can strive, with some guidelines for improving the environmental conditions of storage and display areas containing textiles. Even small efforts to control the most damaging agents of deterioration to textiles, notably light, incorrect RH, incorrect temperature, pests, physical forces and pollutants, will have positive long-term effects on a collection.
Light, Ultraviolet and Infrared
Light is essential to viewing and appreciating textiles, but it fades colours and weakens fibres. Light is the visible part of electromagnetic radiation, a form of energy. It extends from violet through to red. Wavelengths beyond the violet end of the visible spectrum, i.e. ultraviolet (UV), are more energetic and more damaging to textiles than wavelengths beyond the red end, i.e. infrared (IR), which are less energetic. UV and visible radiation have the potential to cause photochemical damage, whereas IR radiation can only produce radiant heat. Damage to textiles depends on the intensity of the light, the proportion of UV radiation, and the length of exposure. The UV radiation in daylight, sunlight, and some electric light sources is a major cause of yellowing and weakening of fibres. Along with light, UV also causes fading or change in colour of many textile dyes, including natural and synthetic dyes.
Mitigating the damaging effects of light and ultraviolet radiation
Light damage is cumulative and irreversible. It is the total light exposure that is important. Total exposure can be understood as illuminance (lux) multiplied by length of exposure (hours). The illuminance, or light intensity, is measured in lux. The object will incur the same amount of damage from exposure to bright light for a brief period of time as from low light for a long period of time. For example, exposure at 100 lux for 400 hours will result in the same damage as exposure at 50 lux for 800 hours. Thus, light damage can be reduced by half by reducing light levels by half (e.g. from 100 lux to 50 lux) or by decreasing the duration of light exposure by half.
Textiles should be exhibited under the lowest light intensity that allows for their aesthetic appreciation. The traditional 50 lux benchmark is adequate for someone under 30 years of age viewing details on light-coloured objects, if very high light levels are not adjacent, and if they are given time to adjust to ambient light. Depending on the sensitivity of colourants used on textiles (consult Michalski Bibliography 1, Table 2, for lightfastness ratings of natural dyes on wool, cotton and silks), a higher lux level, used with caution for brief periods, would enable older viewers and anyone looking at fine or low-contrast details, dark-coloured objects, or visually complex artifacts in a limited time to see them well [~ 4000 lux; each of the above four factors—older viewers, fine or low-contrast details, dark-coloured objects and limited time—increase the benchmark lux level by x3; (50 lux) x 3 x 3 x 3 x 3 = 4050 lux] (Michalski ). Raising the levels only as circumstances demand and then reducing them will minimize cumulative light damage.
Ideally, textiles should not be exposed to any UV radiation from daylight or from unfiltered, UV emitting lamps. If it is not possible to block or eliminate the UV component, levels should not exceed 75 µW/lm (microwatts of UV per lumen of light).
The vulnerability of textile colourants to light varies. To minimize the damaging effects of light on textiles, avoid extremes of light exposure. Eliminate natural light from windows in display and storage areas by covering the windows. Note that the clear, UV-absorbing films available for windowpanes can reduce the amount of UV radiation without reducing visible light. It is important to verify the performance of UV filters and films for lamps and windows before installation, and periodically thereafter. UV meters can be borrowed from CCI (visit Equipment Loans on the CCI website and CCI Notes 2/4 Environmental Monitoring Kit (retired) to learn how to borrow a UV meter).
Turn off lights in display areas during non-visiting hours, and only display textiles for limited time periods, e.g. a three-month maximum. Use visitor-activated light switches. To better control the intensity of light, use lower-wattage bulbs, place dimmers on light switches, and increase the distance between the light source and the textile. Keep a record of the time the textile is on display, the lux level, and the environmental conditions as these will assist in determining annual exposure levels.
Lights should be kept off in storage areas, but lighting for access needs to be at typical office light levels to allow safe and rapid pest inspections and curatorial searches. Storing textiles in closed cabinets or drawers protects them completely from light and UV.
There is currently a confusing array of lamps available on the market. Each type has characteristics that may or may not be suitable for museum display. Lighting for displays is complex and choices should be considered carefully. For more information on current lamp types, their colour rendering index, UV levels, advantages and disadvantages, please consult the tables of light sources (Tables 2a and 2b) under Caring For: Collections - 10 Agents of Deterioration - Light, Ultraviolet and Infrared on the CCI website.
Textiles can tolerate a wide range of RH conditions. It is only the extremes in RH that threaten textile collections. At high RH, fibres swell as they absorb water vapour and, at low RH, fibres shrink as they release it. This dilation occurs primarily in the fibre diameter. Most woven textiles turn this response upside down: the swelling of fibres causes a woven textile to shrink, especially along the warp threads. Nineteenth-century machine-made textiles are especially prone to this form of high RH shrinkage. Aged, embrittled textiles that are restrained, such as framed embroideries, upholstered furniture, and paper maps with fabric backings, may be incapable of withstanding the shrinkage caused by high RH.
High RH allows mould to grow on textiles. At 70% RH, it takes three months or more for mould to develop. At 90% RH, however, mould develops in only a few days. Mould often appears as a white-coloured velvety growth and is sometimes accompanied by a musty odour. Both cellulosic and proteinaceous textiles are at risk. Soils, stains or fabric finishes, such as starch, are attractive to microorganisms as sustenance. The growth of microorganisms causes coloured staining that is often impossible to remove and weakens textile fibres, sometimes to the point of disintegration.
For a more detailed discussion of conditions leading to mould, consult Caring For: Collections - Incorrect Relative Humidity on the CCI website; CCI Technical Bulletin 23, Guidelines for Humidity and Temperature for Canadian ArchivesBibliography 2; CCI Technical Bulletin 26, Mould Prevention and Collection Recovery: Guidelines for Heritage CollectionsBibliography 3; CCI Technical Bulletin 29, Combatting Pests of Cultural PropertyBibliography 4; CCI Technical Bulletin 12, Controlling Museum Fungal ProblemsBibliography 5; and CCI Notes 13/15 Mould Growth on Textiles.
High RH greatly accelerates corrosion of base metals, particularly iron and copper compounds. Brass buttons, steel hooks, eyelets, zippers, etc., especially when associated with salt from human contact or marine environments, can change from being stable for decades to actively corroding within days when RH climbs above 75%.
During winter months, heating without humidification leads to low RH. Between 40% RH and 5% RH, textiles become increasingly brittle, and thus more fragile to handle. On the other hand, low RH has significant benefits for textiles. Light fading is slower, dropping by almost half between 60% RH and 10% RH for some dyes. Insect attack is much less frequent below 40% RH. For wool, this is a particularly important reduction in risk. As long as one refrains from handling weak textiles (such as degraded silks), then low RH is an overall benefit to textile preservation, as demonstrated by the long-term survival of ancient textiles only in arid regions of the world.
In summary, the only form of incorrect RH that should always be avoided in textile collections is damp (over 70% RH). Without damp, there can be no mould, no shrinkage of woven materials (hence no tearing of textiles under tension), no rapid corrosion of associated metal elements, and less of a tendency for dust to cement to fibres. Low RH has significant benefits in terms of reduced pest and light damage, but there is a trade-off with mechanical risks. These mechanical risks can, in turn, be mitigated by careful handling. Avoidance of low RH becomes necessary only where textiles are mixed with other objects that are likely to deform or fracture when exposed to low RH.
The only way to be certain of the environmental conditions in a display or storage area is to measure them using instruments. A hygrothermograph or data-logger is recommended for continuous recording of RH and temperature fluctuations throughout seasonal cycles. Equipment for monitoring light, temperature and RH can be borrowed from CCI (visit Equipment Loans on the CCI website).
High temperatures increase the rate of chemical decay of all materials: double the rate, half the life, for every increase of 5°C. This phenomenon becomes of practical significance only for textiles that are chemically unstable. The classic example in Canadian textile collections are weighted silks of the 19th century. For them, self-destruction is usually already complete (but one can find samples in good condition that were probably kept cold much of their existence). Less vulnerable, but perhaps more prevalent, are cellulosic textiles (cotton, linen, jute) that have become acidified by pollution (and have not been washed), plus all of the 20th century synthetic textiles (rayon, nylon) that can develop acidity internally. While these materials may maintain adequate strength for perhaps a century at 20°C, their lifetime will drop to only two decades at 30°C.
Low temperatures (5°C and lower) have many benefits for textiles. Besides reducing chemical decay, pest frequency is greatly reduced. There is no known danger of even extreme Canadian winter temperatures. In fact, -30°C is the preferred method of non-toxic pest treatment for textile collections, and several studies have failed to find any harmful side effects. (Consult CCI Technical Bulletin 29, Combatting Pests of Cultural PropertyBibliography 4, for details on thermal pest treatment).
In practical terms, low temperature becomes a problem only when it causes high RH and damp. This usually occurs when textiles are stored in a poorly ventilated space (without airtight bags) and one of two things happens:
- the whole space experiences a sudden temperature drop, for example, a poorly insulated house experiences a warm humid afternoon followed by a cold snap at night; or
- textiles are stored in cabinets pushed against a cold exterior wall, such as a basement in summer, or a ground floor in winter.
In summary, in order of importance, watch low temperature situations for damp, and avoid high temperature situations with all of your chemically unstable textiles (e.g. weighted silks, many synthetics, and all unwashed natural fibres with a history of long exposure to air pollution).
Pests are living organisms, such as insects, rodents and mould, which are able to damage materials. Textile and costume collections are often housed in undisturbed, dark environments, which can provide an ideal habitat for insects. Larvae of the clothes moth and the carpet beetle are particularly damaging because they perforate and consume keratinous protein fibre, such as wool. They will attack silk, cotton and synthetics if soils are present or if these fabrics block the way to a food source. Signs of the presence of insects include the actual larvae, their webs and casings (often containing fecal pellets, which may be the same colour as the textile), eggs, and adult insects. Silverfish may damage fabrics en route to a source of food such as the starch sizing on some cottons. Rodents and other animals will gnaw, shred and soil textiles.
Strategies for dealing with pests in a museum include preventive measures like good housekeeping and building maintenance. Avoid using, storing or leaving beverages or foodstuffs in display and collection storage rooms. All new acquisitions and loans should be quarantined, examined and monitored before being introduced into the collection. This allows staff to detect mould and insects.
For information on the formation of mould, visit Incorrect Relative Humidity above.
Dealing with insect and mould infestations promptly will help prevent their spread. Implement an integrated pest management system. Further information on controlling infestations can be found in CCI Notes 3/1 Preventing Infestations: Control Strategies and Detection Methods, 3/2 Detecting Infestations: Facility Inspection Procedure and Checklist, 3/3 Controlling Insect Pests with Low Temperature, Pinniger Bibliography 6, and Pinniger and Winsor Bibliography 7. Also refer to CCI Technical Bulletin 29, Combatting Pests of Cultural PropertyBibliography 4.
Tears, losses, splits and wear can result from previous use, internal stresses inherent in the object, and handling. Sharp creases along fold lines have the potential to become splits because the fibres in these areas are under considerable strain.
Some damage to textiles can be prevented. Historic textiles often appear deceptively strong and resistant, but they are vulnerable not only due to their past history—age, fragility or composition, including combinations of heavy with lightweight materials—but also because they are familiar objects. Handling increases the potential for damage to costumes and textiles. Limit handling textiles and, whenever possible, handle the support or mount rather than the object itself (consult Robinson and Pardoe Bibliography 8 for more detailed information).
Textiles and costumes on display or in storage without adequate support may become distorted by gravity. Custom mannequins for displaying costumes, or padded mounts for storing them, help prevent damage from physical forces (consult Barclay et al. Bibliography 9 and Brunn and White Bibliography 10 for further information). Ensure that mannequins are stable by providing an adequate base or one that can be secured to the display surface. Oversized textiles, such as tapestries, may require custom supports for display and storage, and two or more people to transport or install them.
In transit and shipping, physical forces, such as vibration, impact, pressure, abrasion or shocks, can result in damage. Ensure that textiles are cushioned and secured to their mounts, and provide proper packaging (consult Robinson and Pardoe Bibliography 8).
Gases resulting from industrial, vehicle and other emissions cause degradative chemical reactions, which affect fibre properties. Some products within the museum, such as wood, coatings, acidic tissue paper and other historic objects, can emit harmful gases (consult Tétreault Bibliography 11). Acidity of fibres can also result from the deterioration of the fibre itself and from manufacturing and finishing processes.
Solid particles, such as dust from clothing and soil from the immediate environment, are harmful because they can become trapped in the spaces within and between threads, and on irregular fibre surfaces. Sharp, gritty particles of silica, commonly found in dust, can cut through fibres when handled during storage, display or transit. At higher temperatures and RH, fine dust will cement itself to fibres within a short period and become very difficult to remove. Some particulates absorb pollutants from the environment, which may lead to a harmful chemical reaction to the fibre or the dye under high humidity. Some soils are food sources for mould, insects and other damaging biological activity. Oils deposited from improper handling, water and food stains, and soils from use can oxidize and become set over time, causing disfigurement, weakening and breakage of fibres.
Keep windows and doors closed to minimize problems due to atmospheric pollutants. Any openings to the exterior should be properly sealed. Atmospheric pollutants within the museum can be controlled to some extent by using recommended products (e.g. stable paints on walls and carpeting that does not emit harmful gases) and by enforcing a non-smoking policy. Chemicals, such as paints and cleaning agents, should be stored in a space away from collection storage or display.
Every museum should practice a routine of thorough, methodical inspection and meticulous cleaning. The cleaner the storage and display area, the less chance there is of mould, insects, chemical damage or abrasion occurring. Mounts used to support artifacts in storage and on display should be constructed from stable materials. Objects can be protected from light and dust by covering them temporarily when they are not being viewed.
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By the staff of the CCI Textile Lab
Also available in French.
Également publié en version française.
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