BPG Washing of Books

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The page addresses the use of bulk water, occasionally in combination with various alkaline salts or solvents, to treat the paper of a text block. Alkalinization of text blocks is addressed on the Alkalinization of Books page. Techniques for more local washing and neutralization of individual sheets are addressed on the Washing and Alkalization and Neutralization pages.

Wiki Contributors: Yasmeen Khan, Olivia Primanis, Gary Frost, please add your name 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 Washing of Books." AIC Wiki. June 14, 2024. https://www.conservation-wiki.com/wiki/BPG_Washing_of_Books.

Purpose[edit | edit source]

The removal of degradation products, such as carboxylic acids and carbonyl functional groups, from the cellulose and reintroduce pliability into the paper by the insertion of water molecules into the paper substrate. The main purpose of washing is to remove acidic products from the paper, and therefore alkaline baths form are a part of this chapter because they are used to enhance an acid-base reaction in the aqueous environment. They have the additional benefit of neutralizing the pH of the paper substrate through the introduction of alkaline salts.

Nowadays, conservators view washing as a more complex process and adjust the baths as they proceed through the aqueous treatment with the realization that nearly every bath (regardless of its composition) will result in the elution of degradation products from the paper. The baths will also deposit material into the paper as the wet paper and bath move towards equilibrium and the dynamics of the environment require the water in the paper and the water in the bath to have a reciprocal composition.

Factors to Consider[edit | edit source]

Philosophical Issues[edit | edit source]

Washing treatments can have a significant effect on the connoisseurship of paper-based bound books, influencing their bibliographic description and value as manufactured objects. For example, washing will change paper size and dimension making it harder to work backwards and ascertain the dimensions of the sheets used for imposition of the type and the formation of gatherings. Washing can have an effect on the printing ink and manuscript inks that often appear as annotations and inscriptions. It may also change or remove important historic and forensic evidence from papers. The ramification of treatment should be elucidated clearly so that the decision can be made jointly by the custodian and the conservator.

The major change that has occurred in book conservation is the move away from washing as a standard step in the resewing and rebinding of a book. The stance has changed from the viewpoint of binding a book for posterity (at least 500 years) to seeing the treatment as one in a series of preservation steps. This methodological change has been brought about by both improvements in storage conditions as well as an increasing awareness of the complex systems of deterioration embodied in the various materials of a book.

No longer is a fold test considered a good indicator of a book's usable life, as the gentle rolling action of book pages do not stress the cellulose structure of the paper matrix in the same manner as a fold test.

Results of Spot Testing[edit | edit source]

See also: Spot Tests

Before any aqueous treatment the conservator should perform spot tests to determine the sensitivity of the paper and media to the solution being used. All solutions to be used should be tested. Spot testing gives an approximation of the behavior of the artifact in a bath. Tidelines caused by spot testing are often difficult to remove unless the object is immersed in the solution immediately. Therefore, it is advisable to spot test when the decision to wash is fairly certain.

It is advisable to test book pages in the unprinted margins as well as in the printed area because the wetting out properties of printed paper are quite variable within a printed sheet.

All solutions to be used should be tested at the temperatures they will be used at. If variable wetting out is observed with the testing solutions, it is advisable to spot test with ethanol/isopropanol and water as well so that pre-wetting can be considered an option.

Physical or Chemical Sensitivity of Paper[edit | edit source]

Alteration of Visual, Tactile, and Dimensional Characteristics of Paper[edit | edit source]

Washing will alter the paper appearance, its tactile qualities and dimensions (PCC). The degree to which this occurs will vary and may be controlled by a well-conceived treatment plan.

Shifts in the tone or hue or color of the paper will occur as degradation products are removed from the paper. More vigorous washing methods using alkaline solutions or heat may cause strong color shifts as they remove more material from the paper substrate. In the best cases the paper will be come brighter, but it can acquire a cool gray tone as degraded size is removed. With ground wood paper these shifts can be dramatic as they may cause darkening of the paper and a loss of hemicelluloses that impart certain amount of structural integrity to the paper substrate. If partial washing of the text block is to be conducted then it is vital that there should be visual harmony between the treated and untreated pages.

Changes, bleeding or loss of colorants or brighteners in the paper. Book papers using colored fiber stock may be adversely affected by the presence of water or alkalinity or pre-wetting with ethanol. (Paper colored with indigo dyed fibers have been observed to turn green in the presence of ethanol- YK.) Later printing inks from the 19th century are known to contain colorants that may be soluble in aqueous solutions. (In a student experimental project half the pages of a Bible turned pink during washing due to the bleeding out of the logwood dye.- KP.

Opacity of the paper may be affected due to washing out of fillers. Clay, calcium sulfate and carbonate can all be removed by wash water. Warm to hot water is especially effective in removing calcium fillers from paper. (?) Degraded short fibered papers may actually loose smaller paper fibers that enhance the opacity of those papers, in the bath (YK). Transparentized papers may loose translucency upon contact with alcohol or water (PCC) as the additives that ensure transparency are removed in the bath.

Print impression may be compromised. Washing can diminish print impression in a text block or the plate marks in associated engraved illustrations. Note that the inks and papers used for engravings are often different than those used to print the text itself and will have different treatment parameters. Loss of print impression can be limited by the use of appropriate drying and flattening methods (PCC).

The paper structure will be more open after washing. Depending on the condition of the paper and the washing methods used this may be negligible or, on the other hand, could result in blistering of the surface and loss of material. Extremely damaged sheets of paper should be treated on an individual basis (see Washing) and not as part of the bulk text block treatment. The open texture of the paper can be controlled during washing and mitigated by sizing and appropriate drying methods.

Paper will expand along both the x and y axes during washing. Expansion is not the same along both axes. It relates to the manner in which the original sheet was formed by the papermaker or on the papermaking machine, and to a lesser extent, to the distortions placed in the sheet by the printing process. For modern papers that are often dried rapidly under pressure in an expanded state, washing may cause uncontrollable expansion. Drying does not often return the paper to its pre-treatment dimension and therefore drying should be considered before treatment, especially if the signatures in the text block are made up of paper folded in different directions or if parts of the text block are being treated differently. (Leaf cast pages will invariably be larger than those pages of the text block that have been washed and mended -YK.)

The drying process has a major effect on the visual, tactile and dimensional characteristics of the paper. It is another variable in the treatment protocol that can be manipulated to retain or regain characteristics in the paper that may no longer be visible in the wet sheet. With planning and fore thought, the correct drying techniques can be used to retain print impression, reduce dimensional distortion and minimize the creation of incipient tide lines along the edges of the paper sheets.

Alteration in Sized or Surface-Coated Papers[edit | edit source]

See also: Sizing and Resizing

Papers will become more pliable as they loose stiff degraded gelatin. However, by the same token they will lose their surface protection.

Physical or Chemical Sensitivity of Media[edit | edit source]

  • Solubility or Softening of Media/Breakdown of Binder
  • Other Physical, Chemical, and Mechanical Alterations

Washing Methods, Solutions, and Variables[edit | edit source]


The choice of washing method is based on a confluence of what is best for the object and what techniques and washing solutions are possible in the lab. The benefits to washing a text block, i.e. the elution of acidic chromophoric compounds from the paper and the reintroduction of moisture into the fiber make-up must be weighed against irreversible changes to the paper substrate and the media. Aqueous treatments help to improve the strength, flexibility and brightness of paper. However, it is not recommended that washing alone is sufficient to stabilize deteriorated paper, but must be followed by some alkaline treatment to neutralize the paper or to additionally create and alkaline buffered salt in the paper substrate (see Alkalinization of Books).

All washing methods discussed on this page assume full immersion washing of the text block pages. See Washing for other techniques for washing sheets of paper with specific media or substrate problems that preclude immersion.

Still Versus Running Water[edit | edit source]

Still Water Bath
The amount of bath water and the movement of the bulk water in the bath is controlled by the conservator.


  • You can choose the amount of bath water.
  • You can monitor the pH of bath closely.
  • Fresh solutions encourage more effective washing.
  • You can observe visual change in color of the bath water and use it as an aid in changing bath water.
  • You can agitate the stack of wet papers as needed.
  • You can control and change the type of bath water as needed in subsequent baths.
  • Duration of baths and changes to clean water can be closely controlled based on the elution of colored degradation products from the text block.


  • More time is required to set-up multiple baths.
  • The text block stack has to be handled multiple times.
  • More space is required for washing trays.

Running Water Bath
The amount of bath water and the movement of the bath water are unrestricted by the conservator.


  • Extensive monitoring of the color or pH of the bath water is not required as the bath water is continually refreshed.
  • Agitation is provided by the movement of the running water in the bath.
  • Due to movement in the bath, more degradation products will be removed, but this may be a negligible amount when weighed against the disadvantages.


  • Bath duration will be based on projected needs rather than actual needs of the paper. Paper may be in water longer than necessary.
  • Agitation from running water may cause greater movement of paper stack depending on whether it is washed horizontally or vertically.

Configuration of the Text Block During Washing[edit | edit source]

Open Single Sheets
Single sheets are washed with interleaving to provide support to the paper sheet while wet.


  • provides the most amount of support for the single sheet of paper, which may be an advantage if the paper is weak.
  • Allows for the easy pre-wetting/pre-washing of single sheets with alcohol-water mixtures if there is a possibility of hydrophobic areas on the printed sheet.
  • More water circulating in and around the page which maximizes elution of degradation products.


  • More set up needs. Interleaving doubles the thickness of the text block and therefore more baths and trays may be needed to keep the depths and durations of the baths under control of the conservator.
  • Open pages will expand at different rates and it is difficult, if not impossible to reintegrate the text block, especially the spine folds of the gatherings. and have the fore edge smooth when the book is bound.

Open Sections
Entire sections are washed in the open position with interleaving to provide support between sections.


  • Less interleaving required.
  • The leaves support each other in the bath and it is thought that the pages expand in a more uniform way so that when dry they form a more solid fore edge.


  • Will require more extensive pre-wetting/pre-washing stage as the sheets in the center of each gathering stack will absorb water more slowly. May be mitigated by pre-washing in an alcohol bath.
  • Assumption that the wet sheets in a signature will keep the leaves from floating away when in a bath may be faulty. If that happens then there is no supporting interleaving to help handle the wet paper safely.
  • Less movement of water than washing single sheets.

Closed Sections
Entire sections are washed in the closed position with interleaving in the center of the section and on both sides of the section.


  • Smaller trays can be used which is an advantage if the book is large.
  • Removal of spine adhesive can be accomplished in initial baths.
  • Wet sheets in the gatherings will move less due to the spine fold that keeps them in place. Most effective method of washing sections while minimizing differential edge expansion and contraction within the pages of an individual section.


  • Pre-wetting/pre-washing with alcohol is required as the folded gatherings tend to have many sheets. Fume hood required.
  • Washing may not be as effective due to the thickness of the folded signature and the lack of space at the spine fold. To mitigate this increase in washing time or water temperature may be considered.

Water Source and Additives[edit | edit source]

Though it is acknowledged that paper sheets were manufactured in "impure" water, i.e., water containing contaminants and metals, conservation treatment of those same papers must be undertaken with water that is free of all impurities, unless introduced specifically by the conservator to enhance the treatment.

Tap Water
Unmodified water is used straight from the faucet.


  • Plentiful supply.


  • Variable composition depending on time of the year and pipes.
  • Contains chlorine.
  • Contains metal ions such as copper, iron, etc..

Deionized Water at pH 6

  • Metal ions, chlorine and organic impurities removed.


  • Absence of all metal ions leads to aggressive solution that strips ions from the paper including beneficial ions, such as calcium and magnesium and thus adversely affection the long term stability of the paper.
  • Water quality must be monitored of deionization system using a conductivity meter, (see Monitoring Equipment section.)

Reconditioned Deionized Water
Deionized water that has been through a decalcification column


  • Water less likely to leach out as many beneficial ions such as calcium from the paper substrate.


  • Benefit increases the closer the pH of the bath is to neutral and from the amount of calcium ions in the water.

Calcium Hydroxide-Adjusted Deionized Water
Deionized water adjusted to a pH of 7-8.5 using by adding calcium hydroxide.


  • Calcium adjustment minimized the risk of removing calcium ions from the paper support.
  • Easy to make up calcium hydroxide and add to water.
  • Can increase pH of wash solutions with successive application to gradually modify paper support.
  • Higher alkalinity opens up the paper support so that more effective elution of the degradation products is possible.
  • More effective removal of gelatin size. (Freeman research at Buffalo)
  • Leaves a small amount of alkaline salts in the paper that may help mitigate future formation of acids.


  • Not easy to achieve pH range and harder to maintain once achieved.
  • Certain printing ink and other ink components may be pH sensitive.
  • Once the fiber structure is more open and alkaline it remains more easily accessible to moisture. Resizing should be considered to fill up the gaps in the paper substrate.
  • May cause graying of the paper support.
  • More effective removal of gelatin size.

Ammonium Hydroxide-Adjusted Deionized Water
Deionized water adjusted to a pH of 7-8.5 using by adding ammonium hydroxide.


  • Effectively removes many degradation products especially carboxylic acids from the ends of broken cellulose chains.
  • Especially effective with very dirty paper.
  • Does not precipitate out of the bath or stay within the paper.
  • More effective removal of gelatin size than calcium hydroxide bath.


  • Requires health and safety precautions because it is a corrosive that must be dispensed in a fume hood.
  • May cause graying of the paper support.
  • More aggressive towards colorants in the paper and ink.
  • Difficult to maintain pH of wash bath unless it is covered as ammonia volatilizes.
  • More effective removal of gelatin size than bath calcium hydroxide bath.

Calcium Bicarbonate Bath
(Susan Russick suggested this as an ideal solution for washing, neutralization and the deposition of a small amount of alkaline salts)


  • Can wash media that may be pH sensitive as the bath range is around pH 6.
  • Will remove degradation products.
  • Will deposit calcium ions in the interstices of the paper.
  • Will leave an alkaline salt deposit in the paper to mitigate further acid hydrolysis of the paper


  • Complicated to prepare as it requires specialized equipment.
  • Has a shelf life of weeks depending on storage temperature.
  • Requires careful drying so that there is not pooling and further movement of acidic degradation products in the paper matrix. And also to avoid the formation of alkaline salts on the surfaces of the that dry first upon contact with air (CB.)

Duration[edit | edit source]

Longer washing tends to correspond to more effective removal of degradation products. Regular changing of the bath water will increase the rate of the elution of degradation in bath water as the solution tries to reach equilibrium within the paper substrate and without it. However, the length of time spent in the bath water may adversely affect the media and certain characteristics of the paper itself.

Gradual Increase of pH[edit | edit source]

Some conservators feel that it is best to put a bath into a neutral environment to slowly wet it out and start the elution process. The kinetics of putting an acidic paper in an alkaline bath is considered to be to strong for the paper substrate.

Increasing Water Temperature[edit | edit source]

Washing at room temperature is typical, but baths can also be prepared above room temperature.


  • Increases efficiency (accelerates the reaction rate) and may cut down on washing time.
  • Experiments suggest that increasing the temperature to 86 F/30 C or greater is more effective in removing water-soluble degradation products from the paper.
  • Simmering temperatures are said to improve brightness and flexibility.


  • May affect the appearance of the media.
  • May increase swelling of the paper fibers and cause visual changes to the ink, and media.
  • May increase the removal of fillers and cause the paper to become more translucent.
  • Will increase the removal of non-degraded gelatin sizing.
  • Can cause the paper to shrink
  • May decrease opacity of paper
  • May change give a grey cast to the paper
  • Very aggressive.

Temperature ranges (Fahrenheit and Celsius):

  • "Room temperature" 68°F 20°C
  • Tepid 80°F 27°C
  • Warm 90°F or > 32°C or >
  • Hot 120°F or > 49°C or >
  • Simmering <212°F <100°C

Use of Interleaving Materials[edit | edit source]

Combining Methods and Variables[edit | edit source]

Each object is unique and requires balancing the artifactual and information value of the object with its preservation needs. Having access and the ability to choose from a variety of washing methods to optimize the treatment choices is important. (For examples look in Treatment Variations section.)


  • Can custom-configure the treatment to meet the needs of artifact and find optimum compromise between efficacy and unwanted changes.


  • Requires experience to plan and perform.

Potential Problems in Handling Multiple Sheets of Wet Paper[edit | edit source]

Physical Considerations[edit | edit source]

Damage During Washing[edit | edit source]

Drying Methods[edit | edit source]

See also: Drying and Flattening

Be cognizant that sheets of paper are going into multiple baths and may require rewetting after drying if you have decided on such a treatment path.

Air Drying[edit | edit source]

Possibilities of tide lines. Use of support on only one side of the sheet leads to distortion due to uneven drying. Depending on method of production of the paper the drying might cause greater shrinkage of the paper.

Controlled Drying[edit | edit source]

Materials and Equipment[edit | edit source]

Water[edit | edit source]

Quality/Purity[edit | edit source]

Monitoring Conductivity of Water
(Instructions from Library of Congress Conservation Division)

To assure a level of purity suitable for conservation purposes, use Part's Fisher Digital Conductivity Meter to check the conductivity of treatment water:

  1. Rinse a clean beaker several times with the water to be tested Swirl the water well to remove any residue from the sidewalls of the beaker, as contaminants alter the reading for the sample water.
  2. Fill the beaker with about 200 ml. of water to be tested
  3. Take the sample to the Fisher Digital Conductivity Meter, located near PR&T's reverse osmosis / water polishing system. The left knob of the Meter determines the scale used for the instrumental reading; the right knob turns the Meter on.
  4. Set the left knob of the Conductivity Meter to 200
  5. Set the right knob to MICROMHO (for conductivity)
  6. Remove the glass head electrode from Erlenmeyer storage flask and rinse it thoroughly with water purified by PR&T's system
  7. Immerse electrode head carefully --it's glass-- and completely in water sample
  8. Check the digital readout
  9. After removing electrode from sample, rinse it thoroughly in water from PR&T's system and return it to the storage flask
  10. Turn right knob of Meter to OFF
  11. Record date and conductivity reading on log sheet posted near the Conservation Division DI water system that was the source of the sample.

Conductivity of the Library of Congress Conservation Division water treatment systems is monitored monthly and readings are logged on record sheets posted near each system. Check the log. If there a trend of rising readings is apparent, it's probably time to replace the cartridges.

Notes taken from Cindy Connelly Ryan, Preservation Research & Testing Division and Tse, Season. Water Quality for Treatment of Paper and Textiles, Canadian Conservation Institute Technical Bulletin No. 24, 2001.

Temperature of Water[edit | edit source]

Water Purification Systems[edit | edit source]

Resistivity Meters[edit | edit source]

pH Meters, Electrodes, pH measuring materials

Agents for Limiting Access of Water[edit | edit source]

Enzymes[edit | edit source]

See also: Enzymes

Alkaline Solutions[edit | edit source]

Chelating Agents[edit | edit source]

See also: Chelating Agents

Sinks/Trays[edit | edit source]

Cassette Washing[edit | edit source]

Supports for Washing Paper[edit | edit source]

  • Non-woven materials: Hollytex, Pellon, Remay
  • Woven materials: cotton, linen
  • Plastic supports: Mylar

History of This Page[edit | edit source]

Prior to the creation of the AIC Conservation Wiki, this page was created as "Section 5 - Chapter 1 - Washing" of the Book Conservation Catalog by Yasmeen Khan (compiler), Olivia Primanis, and Gary Frost. For more see: History of the BPG Wiki.

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