TSG Chapter VI. Treatment of Textiles - Section A. Humidification

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Contributors: Originally drafted by Susan Heald and Mary Kaldany. Contributions from: Deborah Bede, Mary Ann Butterfield, Vicki Cassman, Kristin Cheronis, Lucy Commoner, Kathleen Dardes, Patricia Ewer, Susan Heald, Cynthia Hughes, Mary Kaldany, Sarah Lowengaard, Kathy Ludwig, Catherine McLean, Meredith Montague, Denyse Montagut, Patsy Orlofsky, Zoe Perkins, Nancy Pollak, Nancy Rubin, Gwen Spicer, Julia Swetzoff, Cara Varnell, Sara Wolf
Editors: Cynthia Hughes, Sara Wolf Final Revision, April 2, 1998
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Copyright: 2024. The Textile Wiki pages are a publication of the Textile Specialty Group of the American Institute for Conservation of Historic and Artistic Works.
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Humidification

To make humid or perceptibly moist, but not wet or saturated with moisture. To introduce moisture directly or indirectly; to increase the moisture content of a textile.

Purpose

Textiles are humidified to aid in reduction of creasing, wrinkling, and planar deformation. When humidified, hygroscopic materials swell and relax, usually becoming more flexible. Humidification also is used to prepare a textile at ambient RH for aqueous treatment.

Factors to consider in choosing whether or not to humidify

Moisture sensitivity of textile and associated components.

Swelling of fibers may result in mechanical stress, such as planar deformation.

Natural fibers are swelled by moisture.

• Very deteriorated and brittle fibers may not be able to withstand the mechanical stress of this swelling, and may lose their structural stability.
• Swelling of the fibers may allow soils to be driven deeper into the fibers. This may make future removal of these soils more difficult.
• When humidity is introduced locally, those fibers that are humidified will swell, while adjacent fibers will not (differential expansion).
• Varying fiber content may result in uneven mechanical stress. All textile fibers exhibit the phenomenon of swelling to a greater or lesser degree, and this is intimately bound up with the fine structure. When immersed in water there is an alternation in the dimensions of a fiber; this is almost entirely in diameter and only to an insignificant extent in the direction of the longitudinal axis. Swelling of natural fibers in the longitudinal direction is in the range of 1–2% and across the diameter is in the range of 14–19%. The moisture regain of natural fibers is as follows: Cotton – 8.5%, silk – 11%, jute and flax – 13.75%, wool – 14–19%. Wool is very hygroscopic, can take up a greater amount of moisture than any other fiber without feeling damp, and takes up vapor more readily than water (see Trotman, 1990).
• Fibers that have been previously wetted or humidified will take up moisture more readily than adjacent fibers which were never wetted or humidified. This will cause mechanical stress between the two areas.

Some synthetic fibers are adversely affected by moisture. For example, early rayons swell dramatically when wet, resulting in severe fiber deformation. The effect of humidity on other fibers may be less drastic, but still may be harmful.

The textile may be more vulnerable to damage caused by handling when humidified or wet.

• The weight of the textile will be increased by the added moisture.
• Some fibers (proteins) are weaker when wet. This is generally true for any very deteriorated fiber.

Differential expansion of components within the object may set up mechanical stresses.

• Examples could include the differential expansion of textiles with several different weave structures, areas of denser weft, localized applique or densely worked embroidery.

• The core of metal-wrapped, or any other kind of wrapped core thread can swell, resulting in damage to a thin metal foil, or other wrapping.

Non-textile components of the object may be materials that are sensitive to water or water vapor.

• Dyes may bleed.
• There is an increased potential for corrosion of metallic components
• Gelatin-based embellishments, such as sequins, may swell or dissolve in the presence of excess moisture.
• Unstable glass ("weeping glass"), such as in glass beads, will be further deteriorated by moisture.
• Adhesives may be softened by moisture; adhesives may be reactivated and/or move into the fibers. Moisture may cause adhesives to fail between metallics and fibers or other organic substrates.
• Finishes, such as glazes, may be softened by moisture.
• Aqueous based paint media may swell and the paint layer soften with moisture. Oil and resin based paints and varnishes can blanch with moisture.

Interaction with acid pollutants and surface accretions:

Moisture can interact with soils on the surface of the textile, forming harmful substances such as sulfuric acid, altering surface treatments (finishes), and embedding soils.

Effect on appearance of the textile:

• The first wetting will alter the appearance of the textile.
• The use of weights may alter the appearance of some textiles, particularly those with a nap or pile.
• Glazed finishes may be rendered more matte by moisture and/or the use of weights.
• Introduction of moisture may cause stiffening.
• Changes caused by moisture may be permanent.

Loss of historical/archaeological/ethnographic information::

Humidification may remove creases, pin holes, and other distortions in textiles which were a result of original wear or use.

Factors to consider in choosing a technique of humidification

Size of textile

• Chamber or tray methods may be most appropriate for small textiles.
• A dampened carrier (such as muslin) may be more appropriate for large textiles.

Fiber type(s)

• Because of the tendency to spot, mist or spray methods normally may not be appropriate for some fibers, such as silk.
• Fibers which tend to shrink can be dried more quickly and with edges restricted by membranes to prevent shrinking on the suction table.
• Linen, which becomes stronger when wet, can withstand more manipulation during humidification and weighting.

Weave or other structure, and construction

• Pile weaves, thick yarns and dense weave structures are not easily weighted. Suction table techniques may be appropriate for some of these kinds of objects.
• Fine, thin textiles may take on the surface texture of the suction table.
• Three-dimensional portions of a textile need special consideration during weighting.

Nature and location of associated materials

(Surface finishes, dyes, metallics, embellishments)

• Suction table techniques without the use of a membrane may be appropriate if there is the danger of alteration of surface characteristics (see technique information and cautions below on use of the Suction Table).
• Dyes and/or paint often are susceptible to migration during any type of overall humidification. In these cases, localized humidification treatment may be an appropriate option.

Nature, extent and location of area to be treated

Localized methods, such as a steam pencil or damp carrier can be isolated to edges or other areas needing humidification.

Other Factors

Length of time

Time needed to achieve desired results is variable and dependent on such factors as fiber type, age of the textile, severity of distortions, accessibility of distorted areas, and temperature.

Materials and Equipment

Source of humidity

Use distilled or deionized water. Note that tap water may produce undesirable white mineral dust and fragmented mold spores and bacteria (which are not viable, but capable of triggering allergic reactions) into the environment when used in an ultrasonic humidifier.

Standing water. Placed in bottom of basin, sink or tray within a closed environment, but not in contact with the textile.

Fine mist. Directed onto the textile surface or directed into the closed environment with the textile.

• Sprayers/Atomizers.Water is forced through small aperture to create a mist, such as pressurized Dahlia® sprayer (Conservation Materials, Ltd.), air brushes. May also produce undesirable larger droplets.
• Ultrasonic humidifier. Mist directed into environment, created by vibrating metal plate. [N.B.: equipment may need to be modified with a hose or directional attachment.]
• Steam pencil.Used with ultrasonic humidifier used to direct mist at localized areas.

Steam. Higher temperature mists. [N.B. higher temperature mists are more aggressive. Potential damage includes the setting of stains.]

• Warm-mist humidifier.Water boiled and steam directed into closed environment containing textile.
• Clothes steamers. "Jiffy" steamer, hand-held travel steamers. Used locally. [N.B.: steam can carry dissolved minerals and other contaminants from metal reservoir; tend to drip.]

Moistened hygroscopic material. A carrier medium is placed directly against textile, or with vapor-permeable barrier between the textile and dampened material. Carriers include:

• Washed cotton cloth or length of twill tape
• Blotter paper
• Unbuffered tissue
• Paper poultice

Closed environments and Chambers

Confinement of humidity around object being treated.

Small Chambers

• Containers may be constructed out of covered sinks, basins, and trays, and the humidity contained by polyethylene tents, or Mylar® layered above and/or below the object.
• Humidity source: standing water in a basin, ultrasonic mist, or steam.

Large Chambers

• Containers may be constructed as tents on the floor or on tabletops, or include domes on suction tables.
• Humidity source: standing water in a basin, ultrasonic mist, or steam.

Localized Chambers (Inverted beaker)

• Humidity source: dampened blotter located in bottom of beaker
• Humidity container: the beaker itself

Supports

To support the textile during treatment and when returning the textile to ambient RH conditions.

Screens. Rigid frames with plastic, fiberglass or stainless steel screening to fully support the object within the enclosed environment, and to allow faster diffusion of humidity than a solid support.

Padded surfaces.Table top with mattress pad and muslin cover, for blocking, local weighting, and returning textile to ambient RH conditions.

Rigid surfaces. Smooth surfaces such as glass or formica for weighting and returning textile to ambient RH conditions. Table top may be covered with muslin cover or blotters.

Mannequins or padded forms. Covered with absorbent materials such as cotton jersey. For hanging costumes in a humidity tent. [N.B.: padded hangers may cause distortions.]

Barriers - Vapor-permeable

Materials facilitating the passage of water vapor, while physically separating the humidity source from the textile.

• Nonwoven webs. Hollytex® and Reemay® (polyester), Cerex® (Nylon 6,6)
• Gore-tex® membrane/polyester felt laminates. Fluorocarbon polymer membrane allows penetration of water vapor but not liquid water (W. L. Gore and Assoc.)
• Blotter paper (acid-free).

Barriers - Non-permeable.

Materials used to encapsulate the textile and moisture source and/or to slow the rate of evaporation, such as polyethylene, Mylar®, glass sheets, PVC, or latex.

Materials used for support, to ease creases, and to aid in returning the textile to ambient RH

• Blotters. Blotting paper or absorbent non-linting fabric to absorb moisture.
• Padding. Soft nylon tulle, polyester batting, polyester felt, unbuffered acid-free tissue to pad out three-dimensional forms.
• Weights. Shot bags, acrylic and glass sheets, marble or other weights.
• Fans. Low power, to circulate air around the textile when blotters are not practical.

Monitors

Humidity indicator cards or dial hygrometers can be included in an enclosed system (tent, dome, vapor "sandwich") to monitor changes in relative humidity

Humidification - Treatment Techniques - Overall Treatments

Technique: Humidity Chambers.

Introduction of vapor-phase moisture in a controlled environment. This is slower and more controllable than direct humidification. (See also Overall Humidification and Flattening on the Suction Table), below.
Rate of humidification is influenced by: ratio of air volume to water volume; exposed surface area of moisture source; temperature of contained environment (warm water speeds rise of humidity); quantity of hygroscopic materials in the chamber; moisture content of hygroscopic materials in the chamber; nature of moisture source.

• Water (or wet blotters, or wet fabric) is placed in a basin; textile supported above water source.
• Water vapor is channeled into chamber from humidifier /or/ humidifier is enclosed within the chamber.

• Object is placed on floor of chamber (upper surface humidified).
• Object is raised on a vapor-permeable support (such as a screen) to allow humidification of upper and lower surfaces.

Technique: Misting or Spraying

Achieves humidification with control over the amount of moisture, droplet size and uniformity.

• Misting: water sprayed into the air above the textile forming a vapor cloud. Air pressure and water flow from sprayer can be varied.
• Spraying: water sprayed directly onto the surface of the textile.

Technique: Direct Contact Humidification

Introduces moisture vapor by placing dampened hygroscopic material directly on face or reverse of textile.

• Little or much moisture can be introduced through the hygroscopic material, depending on which material is used, including: unbuffered tissue, fabric (such as muslin), or blotter paper.
• Contact is normally maintained between the textile and hygroscopic material by using weights placed over an impermeable barrier material (such as glass, plexiglass or Mylar®).
  [N.B. Unbuffered tissue can be used as a moisture carrier only when extremely small amounts of moisture are required. A mister with an extremely fine spray (such as a Dahlia®) is used to dampen the tissue. This technique is useful when it is important to be able to monitor the textile through the moisture carrier.]

Technique: Vapor "Sandwich" Methods (may also be used locally)

This technique introduces moisture (water vapor) through a vapor-permeable material.

• Porous synthetic non-woven or dry blotter placed between humidity source (damp fabric, dampened blotter) and textile. Textile and moisture system placed between sheets of glass, Mylar®, or polyethylene.
• Use of Gore-tex®-type laminate membrane. [N.B. Large, heavy, or fragile textiles can be more easily humidified from the top surface because one can remove the moisture source and membrane without moving the textile.]

• Felt side wetted out by brushing or spraying water over the surface. Textile and Gore-tex® encapsulated in polyethylene or Mylar® to allow vapor to penetrate the textile.
• From table surface up: humidity source (dampened muslin, dampened blotter), Gore-tex® (membrane side up), secondary barrier (optional - use a non-woven), textile, polyester or Mylar® on top.

Technique: Overall Humidification and Flattening on the Suction Table

Requires a chamber (rigid acrylic dome). Humidity introduced into the chamber (vapor or ultrasonic humidifier).

1. Textile is placed on a vapor-permeable support (such as blotter paper) in the closed chamber.

2. Humidity allowed to increase within the chamber. Low suction introduced to pull moisture through the textile.

3. When sufficient humidification has taken place for the textile to relax, suction is turned off, and the creases are manipulated. Steps 2 and 3 may need to be repeated.

4. A clear, impermeable membrane is placed on top of the textile, suction is re-introduced, and the textile and membrane are left on until the textile returns to ambient humidity.

Technique: Contact Humidification and Flattening on the Suction Table

Introduction of controlled amounts of moisture through a damp fabric carrier in contact with the textile in a contained environment. Very little water is necessary; amount determined by the characteristics of the object (see Factors to consider in choosing a technique of humidification , above). General humidification time is under 30 minutes and is influenced by the amount of water used.

1. A suitable carrier is dampened and placed on the surface of the suction table.

2. The textile is placed on the damp carrier and a clear, impermeable membrane is placed on top, creating a humid microclimate.

3. The textile is allowed to absorb moisture without the introduction of suction, until the desired relaxation of fibers is achieved.

4. The membrane is temporarily removed to allow manipulation of distortions in the textile.

5. Suction is introduced and the membrane is positioned over the textile. The suction and membrane are left on until the textile returns to ambient humidity.

Cautions

• Within a humidity chamber and an acrylic dome (suction table) there is a chance for water to condense on the interior surfaces of the chamber, forming water droplets.
• A textile with a friable paint surface, and textile fibers which are powdery, cannot be in contact with a membrane (suction table technique).

Humidification - Treatment Techniques - Local Humidification/Spot Treatments

Technique: Direct Contact (as for creases and wrinkles)

• Hygroscopic material dampened and placed directly on crease /or/ hygroscopic material dampened and placed both above and below the crease. [N.B. may also be used for adhesive removal.]
  
• Variation: Cotton tape wetted and ironed to barely damp. Mylar® placed under textile, tape placed along crease. Mylar® placed over tape for 10+ minutes. Tape removed, blotters placed below crease, and area weighted locally.

Technique: Localized "humidity chamber" (to soften adhesive; humidify paint media, creases)

Dampened blotter scrunched at bottom of beaker. Beaker inverted over area to be humidified (blotter must be of sufficient size so that it will not fall downwards onto the textile surface).

Technique: Steam for three-dimensional textiles, such as costumes in very good condition

Introduces hot to warm water vapor by drawing head of clothes steamer near surface of textile. Requires a muslin-covered polyester batting pad about the size and shape of a fist. The pad is placed underneath one end of the textile to be humidified (e.g., at the top of a skirt on a hanger or mannequin). Hand-held steamer or nozzle of a tank-type steamer held about two or more inches above padded area. After the textile relaxes (several seconds), steamer is removed and textile allowed to cool in the desired position. Pad is moved down from the steamed area while maintaining a slight tension on the textile. Procedure is repeated moving down the textile in parallel rows.

Technique: Steam for flat textiles

The textile is placed on a padded but firm surface. A hand-held steamer is held several inches from the textile surface. A muslin-covered, polyester batting pad about the size and shape of a fist is depressed against the steamed area for about one minute, until the fibers return to ambient humidity.

Cautions

• Differential stresses between humidified and un-humidified areas.
• Contact humidification in limited areas may produce "tide lines".
• In humidifying one side of a 3-dimensional textile (costume), it may be necessary to separate layers (front and back) by insertion of a vapor impermeable membrane (such as Mylar®).

Crease Removal with Weights

Might be used during or after any of the above humidification treatments to relax creases, wrinkles, or deformations. Amount of weight required determined by desired result (see also Factors to consider in choosing whether or not to humidify, and Factors to consider in choosing a technique of humidification, above.

• Individual weights (such as shot bags) placed locally on textile with a barrier (such as mylar) placed between weight and textile. Blotter paper also may be placed between the weight and the barrier to absorb moisture and soften the edge of the weight.

• Glass or plexiglass sheets placed directly on the textile (additional weight may be provided by shot bags). Blotter paper may be used as a barrier between the glass or plexiglass sheets and the textile to absorb moisture and soften the edge of the weight.

Restoring Three-Dimensional Shape

• Padding of soft, unbuffered, acid-free tissue, nylon tulle, or other supports worked into object gradually during humidification. Supports are left in place while textile returns to ambient RH conditions.
• Variation: Place plastic bag in area to be shaped and stuff with soft padding. The plastic bag provides a smooth surface. Weights can be applied if needed.

References

Trotman, E.R. 1990. Dyeing and Chemical Technology of Textile Fibres. London: Edward Arnold.

Further Reading

American Institute for Conservation, Book and Paper Group.1984. Paper Conservation Catalog. First edition.

Burgeni, A.A. and C. Kapur. 1967. "Capillary Sorption Equilibria in Fiber Masses." Textile Research Journal'.'37(5): 356–366.

Goddard, Patricia. 1989. "Humidity Chambers and Their Application to the Treatment of Deformations in Fabric - Supported Paintings." The Conservator13: 20. (Salt solutions as humidity sources.)

Kyung Sook, Jeon and Ira Block. 1990. "Photodegradation of cellulosics, Part 1: effects of temperature and humidity on tear strength retention." ICOM Committee for Conservation, 9th triennial meeting. Dresden, GDR, 26–31 August, preprints: 302–6.

Hedley, G. 1988. "Relative Humidity and the Stress/Strain Response of Canvas Paintings: Uniaxial Measurements of Naturally Aged Samples," Studies in Conservation. 33(3).

Lennard, Frances.1989. "The Conservation of the United Tin Plate Worker's Society Banner of 1821." The Conservator. 13: 3–7.

Rowland, Stanley P. 1977. "Cellulose Pores, Internal Surfaces, and the Water Interface." Textile and Paper Chemistry and Technology. Washington, D.C.: American Chemical Society. 20.

Stevenson, D. 1990. "Healthily Humid." Canadian Consumer. 2: 31–33. (Information on humidifiers.)

Thomson, G.1986. Museum Environment.London: Butterworths. (Reactions of materials to humidity.)

Weidner, Marilyn Kemp. 1985. "Water Treatments and Their Uses within a Moisture Chamber on the Suction Table," AIC Preprints'.' 13th Annual Meeting, Washington, D.C. 127–140.

Weidner, Marilyn Kemp and Shannon Zachary. 1988. "The System, Moisture Chamber/Suction Table/Ultrasonic Humidifier/Air Filter." Conservation of Historic and Artistic Works on Paper. Symposium '88, Ottawa. 77.

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