BPG Humidification

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Introduction of moisture directly or indirectly into the design and/or paper support.

Conservation of support to realign paper fibers in order to reduce sheet distortions such as cockles, strain or rolling; realign deformations in the sheet such as creases, folds and ridges; reestablish original configuration of the paper, such as original flatness, platemark or embossing.

Conservation of media to consolidate pigments by reviving aqueous binders; relax desiccated gums and resinous lakes, etc. Restore moisture content of solvent treated papers. Soften support so that a new dried configuration can be achieved. Relax sheet in preparation for dry-lining or washing, or suction table work, or expand sheet for stretch drying with edges weighted or confined.

Original Compilers: Doris Hamburg, Dianne van der Reyden, and Tim Vitale
For a full list of the original contributors to this page, see the section below on History of This Page.
Wiki Compilers: Michelle Hamill and Jill Iacchei
Wiki Contributors: Karen Danby, Marie-France Lemay, Roger Williams your name could be here

Copyright 2024. The AIC Wiki is a publication of the American Institute for Conservation (AIC). It is published as a convenience for the members of AIC. Publication does not endorse nor recommend any treatments, methods, or techniques described herein. Information on researching with and citing the wiki can be found on the Reference and Bibliography Protocols page.

Cite this page:

American Institute for Conservation (AIC). "BPG Humidification." AIC Wiki. June 14, 2024. https://www.conservation-wiki.com/wiki/BPG_Humidification.

Factors to Consider[edit | edit source]

When deciding whether or not to humidify and in choosing humidification technique

Sensitivity of Support and Media[edit | edit source]

  • Sensitivity of inks, dyes, media, gums, paper coatings, surface finishes to vapor or liquid moisture
The media's solubility in water should be considered when selecting the method of humidification. Gentler methods of humidification should be used for highly soluble media, which may bleed or sink into the paper support if over-humidified.
  • Paper hygroexpansivity
  • Inherent memory of paper which might be necessary to retain plate mark and/or embossing: hard, calendared surfaces may disturb the surface of some modern papers

Tendency of Support or Media to Water Stain[edit | edit source]

  • Presence of foxing spots
  • Presence of active mold: mold can be expected to proliferate in a humid environment
  • Presence of adhesive residues: when damp the adhesive may be reactivated or possibly move through paper support

Speed of Humidification[edit | edit source]

  • Degree of paper degradation: faster or direct humidification may cause damage to degraded, brittle paper fibers than slower methods
  • Possibility of uneven expansion of supports: multiple sheet constructions, such as chine colle may expand at varying rates and to different degrees and if done, slower humidification may be more controllable
  • Condition of media and relationship to support: media such as oil paint, distemper or heavy gouache on paper may not be well bonded to the support and may expand differently from it

Degree to which Humidification is Desirable[edit | edit source]

Efficiency in Accomplishing Humidification[edit | edit source]

Non-Paper Supports[edit | edit source]

  • Curled or rolled documents on polyester film can often be flattened through counter-rolling without humidification--rolling them in the opposite direction and keeping them in this position with twill tape ties until the documents become flat. This method may not be appropriate for documents with friable or damaged media.
  • Documents and drawings on architectural linen supports can often be humidified and flattened by restraining the edges, lightly misting the supports with water until they expand, then allowing them to air dry. (Suggested by Lois Olcott Price) Placing Hollytex or Reemay beneath the support before humidification is recommended to prevent the damp starch coating from adhering to the blotter below. Some architectural linens have been chemically pre-treated for the diazo photo-reproduction process, according to Lois Olcott Price, and often have slightly cool tone (a hint of blue, purple, or gray) instead of the typical warm white or cream color of untreated architectural linens. Diazo-treated linens have been used for original ink drawings as well as diazo reproductions. Excessive humidification of diazo-treated architectural linens can cause the formation of permanent blue blotches on the fabric. Humidification by light misting may be safest method for these documents.

Materials and Equipment[edit | edit source]

Water[edit | edit source]

  • Should be free from contaminants deleterious to paper such as chlorine, iron, copper, and debris, etc.
  • Should not be allowed to stand for long periods without a fungus inhibitor

Equipment[edit | edit source]

Should not provide sources of iron, copper, chlorine, etc. which may be dissolved into water used for humidification.

Container or Tray[edit | edit source]

  • The container or tray must be sufficient depth that water or damp blotters may be placed at the bottom and a rack suspended above the cover over the container to seal the environment from loss of humidity. Containers may include sinks, heated sinks, enamel trays, photographic trays, wood slats adjusted to the desired size and covered with polyethylene or aluminum battons.
  • A rack is secured above the base of the tray so that it does not come in contact with the water supply yet maximizes the circulation of air within the chamber. Care must be taken that water does not reach the surface of the rack. Racks may be made form light diffusing grates or floating screens.
  • A tray cover is required to seal the environment. The more complete the seal the higher the relative humidity. A transparent cover enables observation of the object during humidification. Covers may be made from glass, polyethylene or polyester film, plexiglas, or other clear, rigid plastic sheet.
  • A garbage can utilizes the same components as a tray chamber, however is an upright system, particularly suitable to rolled items. A plastic garbage can will avoid rust problems and is lightweight
  • Additional variations of the above include jars, domed chambers that traverse the container for hanging folios on threads

Steamers[edit | edit source]

  • Jiffy type steamer
  • Hand held steamer

Spray Equipment[edit | edit source]

Generally designed and sold for spraying paint, though may be adapted for spraying water; sprays may be categorized according to droplet size ranging from fine mists (category I) to coarse sprays (category VI)

Category I: Extremely fine, uniform, tight spray. Circular or oval spray pattern; cannot be adapted to a general misting procedure due to tight spray pattern. Water droplets lighter than dust. Low flow rate

  • Turbine Air Brush
  • Thayer and Chandler Turbine Brush
  • Paasche AB

Category II: Very fine uniformly atomized spray. Water droplets finer than dust. Use higher pressures–20–40 psi:

  • Standard air brush: All tips use larger tips to achieve broad spray; no fan control
  • Paasche H, VL 1–5
  • Thayer and Chandler
  • Precision Sized Spray Gun
Use smaller tips and needles; use no or moderate fan control; flow of the water is controlled by the trigger, bar or button; the air supply is adjusted to between 20–40 psi. The air flow is generally turned on at the very start of the travel of the triggering device used as the flow control. The force of the air atomizes the water as it emerges around the needle, through the opening in the fluid tip, where it is also thoroughly mixed with the air. The relatively high pressure will move the small, low mass (lighter than dust) droplets out so they will not coalesce.
  • DeVilbis EGA series
  • Binks:
  • Paasche Au series and BU series

Category III: Fine, slightly less than uniform, spray: Water droplets larger than dust, some will fall to ground; generally use medium sized tips and needles; 15–25 psi; fan controls to adjust spray pattern.

  • Precision sized spray gun: medium sized tips. Strong fan control.
  • DeVilbis EGA series
  • Binks
  • Paasche BU or CU series
  • Normal spray guns: use small tips and needles on larger guns and large tips and needles on smaller guns. Moderate fan control
  • DeVilbis EGA series
  • Blinks 18 series
  • Paasche 211 series
  • All-in-one (diaphragm) spray units: Noisy and cumbersome. Easy to purchase, inexpensive. Some can produce very nice spray.

Category IV: Non-uniform spray, large to very large droplets present. Water droplets much larger than dust, which may produce 1/16” to 1/4” wet spots.

  • Dahlia sprayer
Keep pumped up; watch out for corrosion.
  • Finger pump mister
Use strong, even strokes.
  • Hand pump sprayers
Use “tightened-down” tip settings.

Category V: Non-uniform spray, very large droplets always present in sizable quantities, which may be up to 1/8” to 1/4” in diameter. Extremely large droplets at end of pump or spray stroke as pressure drops off.

  • Power pak sprayers: use small can of case usually freon. Heat cans in warm water to keep pressure high.
  • spra-tool
  • others
  • Hand pump sprayers:
Use strong even strokes.
“Tightened-down” tip settings best for fine even spray.

Category VI: Extremely large droplets common. Requires special skill to use. Non-uniform spray pattern.

  • Mouth atomizer
  • Brushes
  • Japanese water brush
  • Smaller brushes for local use

Humidification-Treatment Variations[edit | edit source]

Humidity Chamber Techniques[edit | edit source]

Overall introduction of moisture through vapor phase in contained environment. Generally slower and more controllable than direct humidification. speed of humidification will be influenced by: ratio of air volume to water volume; exposed surface area of moisture source; temperature of contained environment (warm water will speed process as well as increase chance of condensation in chamber); quantity of hygroscopic materials in contained environment; moisture content of hygroscopic materials in environment.

  • Water is introduced at the bottom of the chamber either by creating a pool or laying down a damp or wet blotter
  • The object is placed in the contained environment generally resting on a blotter or screen or both. It may be necessary to put the object in a rolled or folded state until it becomes sufficiently limp to allow opening
  • The length of safe and necessary humidification is dependent on the characteristics of the object, as indicated in Factors to Consider; however longer periods of exposure may cause the growth of mold within the chamber. Thymol, ortho—phenyl phenol or borax in the water supply may diminish this threat. Non-soluble media may eventually bleed or soften after long exposure to very high humidity.
  • Condensation of water within the chamber may be a danger to object being humidified. This danger may be minimized by avoiding liquid liquid water which is warmer than the outside environment. The sealing cover can be lined with a blotter or the object can be placed between blotters, although this reduces visibility
A rolling moisture sandwich in action.

Rolling Moisture Sandwich[edit | edit source]

A "rolling moisture sandwich" is used to humidify and flatten groups of rolled paper materials en masse. The technique is adapted from a method originally published in Paper – Line – Light by Eva Glück, Irene Brückle, and Eva-Maria Barkhofen (2012).

Instructions: Williams, Roger. 2022. The rolling moisture sandwich: a method for humidifying and flattening large groups of rolled paper materials. Northwestern University Libraries.

Steam Technique[edit | edit source]

Introduces hot to warm water vapor. This is generally a local treatment which may be used to soften adhesive, but it is also use humidify difficult papers quickly. General Treatment Steps

Humid Suction Table Technique[edit | edit source]

General Treatment Steps

Spray Techniques[edit | edit source]

To achieve slow or quick and efficient wetting with control over the amount of moisture. Need to consider droplet size, uniformity of droplet size, and speed of application.

  • Misting:
The mist should be played out over the support in a cloud; not in a fan (created by allowing air to flow through the fan adjustment valve) as a varnish would be sprayed onto a painting. The density of the cloud can be controlled by the size of the spray equipment, after overall eveness of the cloud has been achieved. Air pressure and water flow can be altered to achieve desired results. Categories II and III equipment is generally used.
  • Spraying Water
Water is usually sprayed in alternating layers (obverse and reverse; with design across design) in whatever scheme is required. Category III, IV and V equipment can be used. Fan controls are used to develop a longer, narrower spray pattern.
General Treatment Steps:
1. The spray is applied in overlapping rows until the first coat of moisture has been applied to the objects.
2. The support is then turned over and the other side is sprayed.
3. The third coat (layer) is applied to the obverse (front) or reverse (back) depending on which side the spray started. Spraying from the back first may reduce the amount of times the front must be sprayed as well as reduce the number of times the wet media is turned face down. It is suggested that the spraying be dividedd into serveral coats, 6–2 to aid in control; Humidification may need to stop after the second or fourth coat of water.
4. Continue as above until the support has become as limp as required.

Brush Application Techniques[edit | edit source]

Brush pattern. Amount of liquid used. Type of liquid.

Blotter Technique[edit | edit source]

May be used locally or overall

Tek-Wipe Technique[edit | edit source]

May be used locally or overall.

Marination Technique[edit | edit source]

Treatment Steps

Poultice Technique[edit | edit source]

Treatment Steps

Bath Technique[edit | edit source]

Treatment Steps

Historical Techniques and Materials[edit | edit source]

Bibliography[edit | edit source]

Banik, Gerhard and Irene Brückle. 2011. Paper and Water: A Guide for Conservators. Amsterdam, New York: Butterworth-Heinemann, 544.
Banks, Paul N. and Norbert S. Baer. 1986. Conservation notes: ultrasonic humidifiers. The International Journal of Museum Management and Curatorship 5 (4): 395-398.
Blaser, Linda and Susan Peckham. 2008. Archives Conservators Discussion Group 2006: overall and local humidification and flattening: tips and tricks. The Book and Paper Group Annual, 25. Washington, D.C.: American Institute for Conservation of Historic & Artistic Works. 43-48.
Caldararo, Niccolo. 1992. Tests on the effects of the use of ultrasound in the humidification of paper. The Book & Paper Group Annual 11: 1-20.
Clarkson, Christopher. 1986. Some innovations at the Bodleian Library. New directions in paper conservation. 10th Anniversary Conference of the Institute of Paper Conservation. 14-18 April 1986, Oxford, England. Institute of Paper Conservation. D75.
Clarkson, Christopher. 1992. A conditioning chamber for parchment and other materials. The Paper Conservator: Journal of the Institute of Paper Conservation 16: 27-30.
Curtin, Bonnie Rose. 1988. Effect on paper pH and alkaline reserve from magnesium bicarbonate introduced via ultrasonic humidification. Book and Paper Group Annual 7:1-6.
Daniels, Vincent. 1998.The effects of water treatments on paper with applied pastel or powder pigment. The paper conservator 22:29-37.
Fairbrass, Sheila. 1987. Ultrasonic humidifier. Conservation news 34:9.
Glück, Eva, Irene Brückle, and Eva-Maria Barkhofen. 2012. Papier - Linie - Licht Konservierung von Architekturzeichnungen und Lichtpausen aus dem Hans-Scharoun-Archiv ; [im Rahmen des Projekts "Architekturpläne des Hans-Scharoun-Archivs. Restaurierung und Digitalisierung einer umfangreichen Architekturplansammlung des 20. Jahrhunderts, April 2008 bis Dezember 2011] = Paper - line - light.
Gowland, Judith and Jane MacAusland. 2003. Some notes on light-bleaching, humidification and steamers. Paper conservation news 106: 4-5.
Hofmann, Christa, Dianne Van Der Reyden, and Mary Baker. 1992. The effect of three humidification, flattening and drying techniques on the optical and mechanical properties of new and aged modern transparent papers. The Institute of Paper Conservation: Conference Papers Manchester 1992. Worcester: Institute of Paper Conservation. 247-256.
Keyes, Keiko Mizushima. 1994. Some practical methods for the treatment with moisture of moisture-sensitive works on paper. Conservation of historic and artistic works on paper: proceedings of a conference, Ottawa, Canada, October 3 to 7, 1988 = Conservation des oeuvres historiques sur papier: les actes de la conférence, Ottawa, Canada, 3 au 7 octobre 1988. Ottawa: Canadian Conservation Institute. 99-107.
Lockshin, Nora, Kathy Ludwig, and Kristen St. John. 2002. "Archives Conservators Discussion Group 2002: humidification and flattening." The Book and Paper Group Annual 21: 57-59.
This is a brief summary of a conference discussion group. Topics include a recent research comparing Gore-Tex, Tyvek, and Reemay methods; discussion of Keepsafe Systems MicroClimate Generator; description of various institutions in-house humidification systems; performing work on oversize documents; and mass-treatment approaches. Includes a bibliography.
Lockshin, Nora, Kristin St. John, and Trujillo, Frank. 2004. Archives Conservators Discussion Group 2003: flattening and drying. The Book and Paper Group Annual 22. Washington, D.C.: American Institute for Conservation of Historic & Artistic Works. 93-95.
Mackay, Gina and Robert Lodge. 1986. Removing severe distortions in a pastel on canvas. The Paper Conservator: Journal of the Institute of Paper Conservation 10: 24-26.
Masson, Olivier and Percival-Prescott. 1989. "L'utilisation de la chambre d'humidification pour le traitement d'oeuvres sur papier" (The use of a humidification chamber for the treatment of works of art on paper), Traitement des supports. Travaux interdisciplinaires. Paris, 2, 3 et 4 novembre 1989. Paris: A.R.A.A.F.U. 207-216.
Masson, Olivier and Westby Percival-Prescott. 1987. The use of lascaux humidification chamber in the treatment of works on paper. Paper conservation news 43: 4-7.
Maxson, Holly. 1987. The design of a collapsible humidification chamber. The Book and Paper Group Annual 6. Washington, DC: American Institute for Conservation of Historic & Artistic Works. 85-88.
Mulhall, Jan. 1989. Gore-tex humidification. Textile conservation newsletter 17: 20-21.
Munn, Jesse. 1989. Treatment Techniques for the Vellum Covered Furniture of Carlo Bugatti.The Book and Paper Group Annual8. Washington, DC: American Institute for Conservation of Historic & Artistic Works. 27-38.
Price, Lois Olcott. 2010. Line, Shade and Shadow: The Fabrication and Preservation of Architectural Drawings. New Castle, Delaware: Oak Knoll Press, HES and DE GRAFF and the Winterthur Museum.
Purinton, Nancy and Filter, Susan. 1992. Gore-Tex: an introduction to the material and treatments. The Book & Paper Group Annual 11: 141-155.
Sugarman, Jane E., and Vitale, Timothy J. 1992. Observations on the drying of paper: five drying methods and the drying process. Journal of the American Institute for Conservation 31(2): 175-197 .
Watkins, Stephanie. 2003. Practical considerations for humidifying and flattening paper. The Book and Paper Group Annual 21. Washington, D.C.: American Institute for Conservation of Historic & Artistic Works. 61-76.
Weidner, Marilyn Kemp. 1986. A moisture chamber/suction table/ultrasonic humidification/air filtering system for use in the treatment of art on paper. New directions in paper conservation. 10th Anniversary Conference of the Institute of Paper Conservation. 14-18 April 1986, Oxford, England. Institute of Paper Conservation. D73-D74.
Weidner, Marilyn Kemp. 1993. Treatment of Water Sensitive and Friable Media Using Suction and Ultrasonic Mist. The Book and Paper Group Annual12. Washington, DC: American Institute for Conservation of Historic & Artistic Works. 75-84.

History of This Page[edit | edit source]

BPG Wiki
In 2009, theFoundation for Advancement in Conservation (FAIC) launched the AIC Wiki with funding assistance from the National Center for Preservation Technology and Training (NCPTT), a division of the National Parks Service. Along with catalogs from other specialty groups, the published Paper Conservation Catalog and the unpublished Book Conservation Catalog were transcribed into a Wiki environment. In 2017, Jill Iacchei and Michelle Hamill reformatted this page by removing the legacy numbered outline format and improving internal links.

Paper Conservation Catalog (print edition 1984-1994)
Prior to the creation of the AIC Conservation Wiki, this chapter was created in 1984 as Chapter 22: Humidification of the 1st edition of the Paper Conservation Catalog, (print edition 1984-1994) by the following:

Compilers: Doris Hamburg, Dianne van der Reyden, and Tim Vitale

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