TSG Chapter VI. Treatment of Textiles - Section G. Drying, Blotting and Blocking

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Contributors: Originally drafted by Kathy Francis. Contributions from: Dorothy Alig, Mary Ballard, Lucy Commoner, Patricia Ewer, Lorna Filippini, Gaelan Gorden, Martha Grimm, Susan Heald, Jane Hutchins, Marlene Jaffe, Mary Kaldany, Susan Mathisen, Jane Merritt, Denise K. Migdail, Meredith Montague, Zoe Perkins, Nancy Pollak, Sara Reiter, Gwen Spicer, Julia Swetzoff, Suzanne Thomassen-Krauss, Deborah Trupin. Final Revision, April 2, 1998.
Editors: M. Cynthia Hughes, Jane Merritt, Deborah Trupin, Sara Wolf.
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Drying of Wet-cleaned Textiles

Drying: To cause or allow to give up liquid or moisture.

Purpose

Textiles are dried in order to return them, after wetting, to their previous dry state of equilibrium in ambient conditions. Drying techniques also may be used as part of a cleaning treatment to remove unwanted, soluble matter from a textile. Manipulation of the textile as part of the drying process (blocking) may allow alignment of elements in a specific orientation.

Freezing may be an interim measure to stabilize the condition of a textile wetted accidentally if immediate treatment isn't possible. Drying is a second choice if a freezer is unavailable.

[N.B. Blotting (the removal of excess liquid) often is the first step of the drying treatment, and so is included in this segment of the Catalog outline.]

Factors to consider in choosing a drying technique

Technique used can influence drying process:

• The rate of drying may be increased or slowed.
• The direction in which the liquid moves through a textile may be influenced.

Textile materials and construction (including fiber type, yarn structure, and supplementary embellishment) will influence drying.

Differences may be seen as variations in the rate of drying and/or direction of liquid movement.

Fiber content, yarn structure and textile processing or finishing will affect drying properties.

• Hygroscopic materials tend to take longer to dry.
• Yarn or fabric sizing or finish may be hydrophilic or hydrophobic and will influence drying.
• Capillary force is affected by fiber diameter, number of fibers or filaments twisted together, amount of twist, yarn structure including number of yarns (plied yarns) and amount of yarn twist and the number and size of interstices within yarns and thus will influence drying.

Fabric structure will affect the length of time a textile takes to dry.

• Open structures expose a greater amount of yarn surface than compact structures and thus may dry more quickly than compact structures in similar circumstances.
• More complex structures, especially those in which supplementary elements create a multi-layered fabric, will take longer to dry than fabrics of simple structures in similar circumstances. Individual layers may act to impede uniform drying.
• Since pile yarns tend to dry first, liquid moves from the foundation fabric to the pile.

In otherwise comparable circumstances, fabric thickness has an effect on the length of time a textile takes to dry.

• Thick fabrics (ie. pile carpets, hooked rugs) will generally dry more slowly than thin ones.</la>
• Multi-layered fabrics and textiles of uneven thickness (ie. quilts, garments, raised work techniques), may dry unevenly due to differences in thickness. This is also the case (but to a lesser degree) where additional fabric thickness is present due to seams, hems, etc.</la>

• Borders or outer edges tend to dry before center portion of the textile.

The size of a textile influences options for drying

There are limited options for drying large textiles. Smaller size often allows for using more controlled drying techniques such as suction table drying. Large textiles may be cleaned and dried in sections on a suction table.

Preservation of fabric surface

It is important to preserve the nature of the original fabric surface. (If it is not possible, one should consider if the piece should be wetted at all.) The characteristics of the fabric surface will influence the choice of a drying technique and may affect the length of time a textile takes to dry.

• Flat, smoothly finished fabrics may be kept flat and smooth if positioned for drying on a smooth surface.
• The surface of a fabric with texture, dimension, or embellishment may be best protected from deformation if dried front side up.
• Pile fabrics may be best protected from surface deformation if dried front side up.
• Complex structures, especially those in which supplementary elements have a greater predominance on one side, should be dried with the side of the greater predominance or layering of elements up. (i.e. The layers of supplementary brocading weft floats on reverse of brocaded silks should be dried reverse side up.)

Special considerations for surface embellishment, fringes and trims

• Embellishment may demonstrate different drying behavior from the foundation fabric and may behave like pile yarns. Differences may depend on variation in materials or construction. Generally speaking, raised embellishment may be best protected from deformation if dried front side up. [N.B., if embellishments are adhered, the object may respond differently than if embellishments are stitched to the object.]
• Liquid will move from wetter areas towards non-metallic edge trims or fringes which tend to dry first.
• Beads, sequins, and metal decorations may affect or influence drying techniques.

Dyes may bleed and fibers/fabrics may form brown staining during drying.

One goal in drying textiles is to remove moisture as quickly as possible in order to reduce oxidation of fibers, brown line staining (due to oxycellulose migration, breakdown of impurities, etc.), and dye migration. The use of drying cloths has been effective in reducing damage due to the latter two factors. The choice of the type of drying cloth is important to avoid slowing drying time, thus fostering the conditions under which brown line staining and dye migration are a great risk.

Choice of drying technique is limited if dyes are known or suspected to bleed.

• Techniques utilizing supplementary drying cloth or blotter paper may help to control dye staining damage and may reduce dye staining from previous water damage.
• Techniques that help to control the direction of drying may help to control dye staining damage.
• Techniques that accelerate drying may be desirable as they may limit dye staining damage.

If soluble soils and degradation products are present in the fabric or water they may be deposited as staining on the fabric during drying.

• Cellulosic textiles with fabric or batting that contains bits of "trash" (plant matter such as pieces of stem, leaf and boll that appear as brown flecks) may release brown color and stain the textile during drying.
• Oxidized cellulose (oxycellulose) is usually water soluble. Uneven moisture levels due to uneven wetting (water damage) or uneven drying can cause these by-products to migrate to the interface of the nearest wet\dry area through capillary action, causing brown line staining. Other conditions thought to favor brown line staining are: slow drying, low air circulation, and repeated wetting and drying.

Textile artifact damage may influence drying behavior.

• Surface abrasion may cause surface yarn fuzziness that may behave similarly to a napped or pile fabric. Abraded areas (or the abraded surface) may dry first, and liquid will wick from wetter areas toward those areas.
• Frayed edges will tend to dry first and behave as a wick.
• Holes create damaged edges in the interior of a fabric, which tend to promote uneven drying.

Ambient conditions

• Textiles dried at or near ambient conditions will retain more moisture than they had before wetting.
• Increasing air temperature and/or air movement accelerates drying. [N.B. dehydration of fibers can result from air temperature that is too high.]
• Textiles dry more quickly in conditions with lower relative humidity.
• Rapid drying in low ambient relative humidity conditions gives the textile a relatively high moisture regain capacity. Slow drying, with little or no air movement favors hydrolysis and results in low moisture regain capacity.
• Ideally, if warmer than room temperature air is used for drying, the air temperature should be lowered to room conditions as soon as the surface of the textile appears dry and until the drying process is complete.

Materials and equipment

Supports

Screens. Rigid frames with polyester, polypropylene or stainless steel screening to support the textile, and to allow greater air circulation, thereby hastening the drying process.

• Some saran screens have been observed to release an oily substance.
• PVC-coated fiberglass screens (grey hardware screening) have been observed to release a black gummy substance, to crock a lead-based pigmentation, and to plasticize plastic components or painted surfaces when in direct contact.

Rigid surfaces. Any flat, hard, smooth surface to support the textile (ie., bottom of wash tank, Mylar® and table top, piece of glass, acrylic). Some surfaces (such as a paperboard panel or polyethylene foam covered with plastic) allow for blocking the textile and holding the established position with corrosion-free pins into the support surface.

Absorbent surfaces. An absorbent material may be either stretched onto a rigid frame or placed over a rigid surface.

Mannequin supports. These may be full body forms or partial forms (such as shoulder or waist supports).

Custom supports and stuffing materials. Specially shaped supports may be made for three-dimensional items. The support surfaces may be composed of screen, a rigid substance or an absorbent material, or polyethylene bags stuffed to a customized shape.

Supplementary materials used to absorb or wick liquid water away from the textile

Materials used to absorb excess water before drying (blotting)

• Washed, lint-free cotton or linen toweling.
• Washed cotton mattress pads.
• "Super absorbent", disposable diapers for emergency situations, such as damage from leaks, floods, etc.
• Unbuffered blotter paper or tissue; chromatography paper [N.B., alkaline buffered materials may cause dye bleeding and may adversely affect protein fibers.]
• Washed sponges.

Materials used during the duration of drying ("drying cloth") to wick moisture and any matter carried with it away from the textile. The choice of drying cloth material should balance the need to dry the textile quickly and prevent damage due to brown line staining and dye migration. Open-weave fabrics such as cheese cloth allow for air circulation and evaporation in addition to the contact necessary to wick degraded cellulosic material and fugitive dyes. Isolated areas of fugitive dye may be treated with a perimeter wicking material that reduces damage to the textile and does not interfere with air circulation, evaporation, and quick drying.

• Washed cotton cheesecloth (several washings may be necessary to reduce fiber shedding).
• Washed cotton sheeting.
• Washed cotton netting.
• Poulticing material (a finely divided and absorbent material placed on the object while wet with water or solvent and allowed to dry in place). Ideally a poultice absorbs unwanted material from the artifact through capillary action. Poulticing materials include paper or fiber pulp, and finely divided cellulose powder separated from the textile by tissue so that the powder does not become lodged within fibers and yarns.

Equipment used to affect air movement, air temperature, or relative humidity of air

• Fans.
• Hand held hair dryers.
• Dehumidifiers.
• Drying chambers.
• Suction tables and suction discs.

Blotting

The use of absorbent materials to remove excess liquids from a textile as the first step of the drying treatment in limited areas or across the textile as a whole. As the absorbing material becomes wet, it is replaced with dry material, until the excess liquid has been satisfactorily removed from the textile.

Blotting techniques for removing the maximum amount of liquid

• Absorbent material is placed above and below (if possible) the textile. Slight pressure is applied with the hands to speed the removal of the liquid.
• If the textile is in good condition, absorbent material may be placed on the textile and the two are rolled to produce greater contact between the materials.
• Absorbent material is laid across the textile and used to wick excess liquid away from the textile.
• Absorbent material is placed at the edges of the textile to wick excess liquid away from the textile. [N.B., The torn edge of blotter paper placed at the edges of a textile promotes rapid wicking of liquid away from the textile.]

Blotting techniques and drying cloths

There are several approaches to combining the use of drying cloths with blotting techniques:

• Drying cloth placed on surface of textile after initial blotting. Textile is blotted minimally and allowed to retain excess moisture so that the maximum surface contact between textile and drying cloth can be achieved and maintained until the textile is dry.
• Drying cloth placed on surface of textile and blotting materials placed over drying cloth. [N.B. when removing blotting materials care must be taken to prevent disturbing the contact between the textile and the drying cloths.]
• Drying cloth placed on the surface of the textile after thorough blotting. Smooth out the drying cloth to establish contact with the textile.

Blotting techniques applied to limited areas of the textile

Tissue is placed on the surface of the textile, and poulticing materials, such as analytical filter paper pulp, paper or fiber pulp, or finely divided cellulose powder placed on the tissue to absorb unwanted materials from the textile and deposit these materials in the poulticing material through capillary action.

Blocking

The re-alignment of fabric elements to their intended orientation, through controlled manipulation or pressure, to flatten surfaces or minimize deformations during the drying treatment. The warps and wefts of woven textiles are aligned perpendicular to each other to minimize wrinkling during the drying treatment; seams and design elements should be aligned to prevent the piece from drying in a distorted position. A textile should be aligned when wet; if the piece is aligned when damp or partly dry, the yarns may be pulled apart causing irreversible distortion. Water can be reintroduced to the textile during the blocking process by spraying or applying with a brush. A pool of water should be formed so that the textile can "swim" while it is adjusted so that there will be little tension between it and the support surface.

Factors to consider

Degraded fabrics are weaker when they are wet, as are wool and rayon.

Materials for blocking

• The surfaces used for blocking should be larger than the textile, and may or may not accept pins, depending on the technique of blocking to be used. Surfaces that can be pinned into include screening with a dense grid, heavy paperboard panels, or polyethylene foam or homosote panels covered with plastic or white contact paper.
• Stainless steel pins
• Weights (such as glass plates)

Technique for blocking using pins #1

1. Fabric elements are aligned in desired orientation on the blocking surface.

2. Working from the center of the textile, pins are preferentially placed in structural voids or interstices of warps and wefts to avoid breaking yarns. Pins are placed at an angle to the board with the heads turned outward toward the edges of the textile.

3. Drying should be closely monitored so that pins can be removed before any shrinkage can occur around the pins. This could cause breakage of elements or shifts in element alignments resulting in enlargements of interstices.

Technique for blocking using pins #2

1. Working on a dense grid screen, the warps and wefts of the textile are properly aligned.

2. Stainless steel pins are pushed straight down through the textile (between the weaving elements) and into the screen. This creates less tension than placing pins at an angle, if the textile undergoes dimensional changes during drying.

Technique for blocking on a rigid surface (for a relatively fine, flat textile)

1. An adequately wet cotton, linen or silk textile may be aligned by gentle smoothing with the fingers, a wide Japanese paste brush, and\or a brayer working from the center out and removing all air bubbles under the textile.

2. Excess water that has been brushed out beyond the edges of the textile should be removed by blotting the rigid surface dry. [N.B. the textile must be quite wet in order for the rigid surface to adequately "grip" the textile in its aligned position; blotting on the surface of the textile may cause the textile to lose contact with the rigid surface before the textile is completely dry.]

3. The side of the textile that is flat against a smooth, rigid surface will be perfectly smooth (as if ironed after drying), while the face up side will have more texture after drying. (Drying on a screen will not provide a smooth surface and may leave an imprint.)

Technique for blocking with weights #1

1. Elements are aligned in desired orientation on a flat, rigid surface.

2. Weights are placed along the edges of the drying textile to restrain its movement. Uneven drying of the textile may result when weights are placed on only part of the textile. Weights must be non-absorbent (such as glass plates) or else blotter paper, Reemay®, or similar material should separate the weight from the textile.

3. The use of weights will prolong moisture retention of those areas covered by the weight. Monitor drying closely and shift or remove weights as soon as the textile appears dry. This will insure that the uncovered areas do not complete the drying process before the weighted areas are exposed to the air.

Technique for blocking with weights #2

1. Elements are aligned in desired orientation on a flat, rigid surface.

2. Netting is placed over the textile, extending beyond the edges of the textile.

3. Weights are placed on the netting just beyond the edges of the textile.

Technique for Blocking on a Suction Table

A wet textile may be blocked on a suction table prior to drying (on the table or by another method).

1. If necessary, place a layer of muslin on the surface of the table.

2. The textile is aligned in the desired orientation before suction is applied.

3. Water in the interstices, fibers, and pores will act as a membrane allowing the textile to be blocked under suction without a top membrane.

4. Stronger textiles which can tolerate a membrane over their surfaces can be put under suction for a few minutes (10–20) to flatten as well as achieve proper shape, size and alignment before drying.

Drying - Treatment techniques

Technique: Air drying flat textile on raised screen

Allows air circulation around textile to speed drying. Textile may be covered on one or both sides with supplementary material, such as a drying cloth. [N.B. screen may leave an imprint on a textile in contact with screen surface.]

Technique: Air drying flat textile with bottom surface of a rigid, smooth and non-absorbent substance

Promotes wrinkle-free drying primarily from the top surface of the textile, which may be uncovered, or covered with supplementary material such as a drying cloth, blotter or tissue.

Technique: Air drying flat textile with supplementary material

Textile is in direct contact on one or both sides with supplementary absorbent material larger than the textile itself, such as a drying cloth. Promotes wicking of water (and any matter carried with it) from the textile to the drying cloth.

Technique: Air drying flat textile with fringes and trim

Supplementary wicking materials are secured to the perimeter of the fabric to promote wicking. Blotter paper should extend beyond the fringes to encourage the deposition of any unwanted materials in the paper beyond the edges of the fringe.

Technique: Air drying pile textile with strips of supplementary material as wick to control dye bleed

Before wetting, strips of absorbent fabric are stitched to textile, between rows of pile along boundaries of problem colors. Edges of fabric strip extend upward beyond textile surface.

Technique: Drying flat textile on suction table

Following wet treatment, textile is positioned on suction table and left to dry with suction turned on.

• A porous support layer may be needed between the textile and the surface of the suction table to prevent a screen pattern from appearing on the textile and/or to adjust the capillary action and suction of the table.
• It is desirable to use a light-weight, air permeable fabric (such as thin archival quality non-woven felted polyester) on top of the textile to act as a filter for the large quantity of air passing through, to keep out airborne particulates.

Technique: Accelerated drying by use of a fan or hand-held hair dryer

[N.B. Air flow should not be aimed directly onto the textile as it may cause the textile to flutter and may blow airborne particulates onto the surface. When using accelerated air drying, it is advisable to use a drying cloth.]

• Fan is used on low speed, and produces air movement to accelerate drying.
• Hand-held hair dryer produces heat and air movement to accelerate drying. (Use on "warm" setting, if possible.)

Technique: Drying garments and other three-dimensional textiles

Drying delicate or fragile garments on a flat surface:

1. Garment is positioned on screening, absorbent or non-absorbent support.

2. Padding, usually net fabric or fabric-covered polyester batting, is used to shape garment and reduce wrinkles. Hand manipulation may be used to smooth fabric. Large areas with limited access can have a plastic bag inserted and gradually filled with batting to develop a shape. Example: a mutton sleeve.

3. Supplementary materials such as drying cloths may be used. The drying cloth must be in direct contact with the garment. Cheesecloth conforms to padded forms well and can be misted to achieve good contact to ensure that capillary action wicks soluble soils to the cheesecloth surface and not the garment surface.

Drying stable garments on a form (shoulder form, partial or full mannequin form).

1. Drying usually begins on a flat surface.

2. Garment may be partially or fully padded with net fabric or fabric-covered polyester batting to shape.

3. When partially dry, if the garment is in good condition, it may be transferred to a three dimensional form or partial form to complete drying. [N.B. This is the only situation in which a damp textile is moved before it is completely dry

Isolate areas around steel buttons, buckles, or hooks and eyes, with dry cleaner's foil, muslin bags or Mylar®, to prevent rust or subsequent staining of adjacent fabric.

Technique: Freeze drying

Freeze drying can be used for fragile textiles like archeological fragments. In freeze drying, the textile is frozen before drying takes place by sublimation. The freezing process is critical, and a point at which the speed of determines the size of the ice crystal formed, which in turn can pose a potential threat to the structure of the fibres. The faster the freezing, the smaller the ice crystals, meaning less damage is likely to occur. The subsequent drying process is characterised by low temperatures and low air pressure. Although the drying process can take place at atmospheric pressure (1013 mbar), reduced pressure is often used in practice to speed up the process (vacuum freeze drying). One advantage of drying by sublimation is that surface tension is reduced, whereby there is less chance of the risks associated with air drying. As mentioned, the main risk factors associated with freeze drying are damage from ice crystals or too strong a vacuum, but there is also a risk or removing too much moisture from an object. Problems to look out for during drying are shrinkage, stiffness, damage to fibres, distortion and puckering of the fabric.

Further Reading

Burgeni, A.A. and C. Kapur. 1967. Capillary Sorption Equilibria in Fiber Masses. Textile Research Journal37(5): 356–366.

Harris, M., ed. 1954. Harris' Handbook of Textile Fibers. New York: Interscience Publishers, Inc.

Hearle, J.W.S. and R.H. Peters. 1960. Moisture in Textiles. New York: The Textile Institute and Textile Book Publishers, Inc.

Hutchins, J.K. 1983. Water-Stained Cellulosics: A Literature Review. Journal of the American Institute for Conservation 22:57–61.

Michalski, S. 1981. Suction Table History and Behavior. AIC preprints. American Institute for Conservation, Ninth Annual Meeting. Washington, D.C.: AIC.129–136.

Michalski, S. 1984. The Suction Table: A Physical Model. AIC preprints, American Institute for Conservation, Twelfth Annual Meeting. Washington, D.C.:AIC. 102–111.

Morton, W. E. and Hearle, J. W. S. 1975. Physical Properties of Textile Fibres. Manchester: The Textile Institute.

Rice, James W. 1972. Principles of Fragile Textile Cleaning. In Textile Conservation, ed. J.E. Leene. Washington, D.C.: Smithsonian Institution Press. 68–70.

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.

Stone, J.E. and A.M. Scallan. 1966. Influence of Drying on the Pore Structures of the Cell Wall. In Consolidation of the paper web, Trans. of Symp. Cambridge, Sept. 1965, ed. F. Bolam. Vol. 1. London: Tech. Soc. British Paper and Board Makers' Assoc., Inc. 145–173.

Sugarman, J. E. and Vitale, T. J. 1992. Observations on the Drying of Paper: Five Drying Methods and the Drying Process." Journal of the American Institute for Conservation." 31:175–197.

The Textile Institute. 1975. The Identification of Textile Materials, 7th edition. Manchester, UK: The Textile Institute.

Sjoukje Telleman, Emmy de Groot, Ineke Joosten, René Lugtigheid and Maarten R. van Bommel, 2022. The Texel Textile find revisited: the testing of cleaning and drying process fro historical wet rags. In Journal of the Institute of Conservation. Vol 45, N.1, pp. 3 - 17.

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