Study on the off-gassing and storage environment in the conservation of Japanese
woodblock prints
浮世絵の保存におけるオフガス特性とその収蔵環境に関する研究

ギマラエス ロメロ アナ テレサ
Guimaraes Romero, Ana Teresa
1. Introduction
Organic acids – mainly acetic acid, formic acid – areamong the many volatile organic compounds (VOCs) thatprints and contributing to their acidification.

are naturally off-gassed (emitted) from aging paper andwood objects, and their potential application as diagnostic
tools to assess the conservation state of paper-based

Hiroshige Museum of Art (Tendo, Yamagata)
The second chapter of this dissertation introduces theoff-gassing measuring method used through this research

cultural property has been suggested before.1,2 In addition,acetic acid has been singled out as specific degradation
marker of acidified paper, as this VOC is often foundand offers the first indications of storage influence in theprints’ acidic off-gassing. A special apparatus made ofacrylic sheets to firmly secure the print during

present in comparatively higher concentrations inrepositories containing paper-based collections.3,4
As such, this research began with the goal of measuringmeasurement was built. Kitagawa™ precision gas
detector tubes no. 910 for Organic Acids (acetic acid +formic acid) and no. 900NHH for Ammonia, mounted onorganic acids off-gassed from Japanese woodblock prints(ukiyo-e) as a potentially non-destructive way ofaccessing their state of acidification. Such method

ASP-1200 model air sampling pumps, were used tosample both acidic and alkali gaseous emissions. The first
field experiment using this measuring method occurred in

could’ve been employed as a preventive measure todetect ongoing acidification in woodblock prints, as wellas other paper-based cultural properties, before visible

the Hiroshige Museum of Art in Tendo, Yamagata, wherea woodblock print attributed to Toyokuni III & Hiroshige
II that had been part of the museum collection for at least

signs of degradation appear.

50 years was measured for acidic off-gassing (Figure 1).

2. Measuring off-gassing: Preliminary testing atHowever, as it will be demonstrated in the following
chapters, no significant correlation was found between
organic acid emissions and pH of prints. It was also
observed that acetic acetic-concentrated storage spaces
were not necessarily an indication of acidic/acidifying
paper collections. Considering the findings gathered inthis research, this dissertation theorizes that acetic acid isprone to accumulate inside closed spaces with low
air-exchange rate due to its relative stability as anend-reaction product of hemicellulose decomposition.
This phenomenon is of particular importance to ukiyo-ecollections. Accepted storage practices that protect thesensitive prints from damaging UV rays, humidity
fluctuations, dust and pests, involve storing the prints inindividual folders or semi-airtight storage boxes forprolonged periods of time. These practices may,conversely, aggravate the acidic off-gassing of woodblock

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Figure 1. A and B: Outlook of off-gassing measuring method C:
Detector tube after measurement.

When this measuring method was preliminarily tested
in laboratory, different off-gassing values were collected

from different areas of the same print. However, theresults obtained in the Hiroshige Museum wereorganic acids on the print’s off-gassing.

surprisingly homogenous. In addition, it was found that

4. The storage environment of woodblock prints –the print’s organic acid off-gassing values were similar tothe values of the folded Japanese paper that wasenveloping the print in storage. Further investigation

Influence in the acidic off-gassing of storage items(Part I)A field experiment took place in the University of

revealed that the museum’s storage room had aconsiderable concentration of acetic acid in air comparedto the other museum’s rooms.

Tsukuba Library, with the goal of assessing how thestorage environment was affecting the off-gassing of a
selected ukiyo-e print from their collection.

3. Correlation between off-gassing and acidification ofwoodblock prints

The organic acid concentration in the Library’s storage
room and inside a wooden storage box housing a Meiji
period ukiyo-e collection was measured, after which one

This chapter elaborates on the set of experiments thattook place when the research goal was to hopefully find alinear correlation between off-gassing behavior andprint was selected for a VOC mitigation experience using
a fan-filter unit (FFU). It was found that, despite thestorage room concentration being within accepted

acidification, as well as the findings that redefined theresearch goal towards a direction that focused on theeffect of the storage environment in organic acidthresholds of museum indoor pollution,6 the organic acidconcentration inside the storage box was three times
higher the room’s concentration.

accumulation inside containers with ukiyo-e collections.
Surface pH values and organic acid and ammonia gas
emission concentrations were collected from six

The VOC mitigation experience which followed,
consisted of sealing the selected ukiyo-e print with asmall-sized FFU inside an Escal® plastic bag, so to create

woodblock prints for a period of one year. Off-gassing
measurements were performed with the same instruments
as previously described, and mapping of surface pH

a closed, recirculating stream of clean air to rinse the print
and eliminate its organic acid emissions (Figure 2). Afterbeing rinsed, the print was returned to its original storage

values was done by agar gel pellet sampling method,
based on the technique developed by researchers at theSmithsonian Institution.5 Lastly, the environment insideplace (inside the wooden box), and organic acidre-emission was measured after 20 days. The procedure
was repeated, but in the second time, the rinsed print was

the storage folders of each print was assessed for acidity
using acid-detector (A-D) strips, developed by Image
Permeance Institute.

put in a different storage place with clean air and organicacid re-emission was measured after 25 days.

Combined results from these experiments indicated anaccumulation of acidic vapors inside storage folders. The
folders with fewer openings had a stronger acidic
environment inside. In addition, it was observed, after
studying the acidification patterns of the prints, that thelesser acidified areas were located closer to openings intheir storage folders. No significant correlation was foundwhen organic acid off-gassing values were plotted against
correspondent area pH values; however, moderate

Figure 2. Design of the VOC mitigation experiment with an FFU.

correlation was found when the former were plottedagainst change of pH value in a 3-4 month interval.
Finally, it was concluded that a varying percentage ofResults from this experiment indicated that the woodenbox storage was affecting the print’s acidic off-gassing. Itmeasured organic acids emitting from the prints were ofexogenous origin (room environment). The following
chapter further explores the influence of environmental

was found that, after the 20-day wooden box storage
period, the print was emitting 32 ±19%. more organic
acids compared to a 25-day storage period in a clean
Summaries of Academic Theses 2021

environment. Results also revealed that off-gassing
behavior was not uniform, as different areas of the print

which traps organic acids off-gassed from both prints andstorage materials inside with nowhere to “escape”, as theemitted different concentrations of organic acids,room’s ventilation system does not reach to the interior ofsuggesting that pigments and/or relative locationinfluenced off-gassing behavior.

these boxes. It was also concluded from this experimentthat the FFU system had a moderate success in mitigatingorganic acid concentrations inside the box even though it

5. The storage environment of woodblock prints – On
the formation of microclimates inside storage boxes
and mitigation strategies (Part II)

did not offer a permanent solution.

This chapter discusses a similar investigation andexperiment as the previous chapter, this time focusing on
the storage materials of an Edo period ukiyo-e collection,
also housed in same storage room in the University ofTsukuba Library. Instead of a wooden box, the storage
materials investigated here consisted of an acid-free
cardboard archival box and a Japanese paper folder. The
objective of this experiment was to gain a better
understanding of the formation of these microclimates

Figure 3. Re-emission of organic acids (µg/m3) during theand evaluate the FFU system as mitigation strategy whenemployed on the storage materials.
The storage environment was first assessed for organic

follow-up period.

acid content, and once again, a similar organic
acid-concentrated environment was found inside thearchival box, with about 3 times the room’s concentration.

acid-concentrated environment
A laboratory experiment aimed at observing the impact
on pH and off-gassing in prints after exposure to an acetic

It was also found that the print in the middle of the stack
was emitting more organic acids than the other measured
prints. It has been suggested in published research that

acid-concentrated environment was developed anddescribed in this chapter.
Samples representing common characteristics of

VOCs migrate between stacked sheets of paper until they
become trapped in the middle of bottom sheets,7 and dataobtained from this experiment similarly hints at VOC

ukiyo-e prints were prepared in laboratory, using
non-bleached Japanese paper sized with an alum+nikawa
solution and colored with pigments. Seven groups ofaccumulation happening in the middle prints.
The storage materials were then rinsed off organic

samples were prepared: 1) unsized paper samples (A-Pa);2) sized paper samples (B-Do); 3) sized paper samples w/

acids by FFU system (as previously described), afterindigo (C-In); 4) sized paper samples w/ Prussian blue

which they were returned to their original positions in the(D-Pr); 5) sized paper samples w/ orpiment (E-Or); 6)

storage room with the prints inside. For a follow-up
period of 5 months, organic acid content inside thesized paper samples w/ red iron oxide (F-Re), 7) sizedpaper samples w/ red lead (G-Mi).

archival box and paper folder was measured.
Results from the follow-up measurement revealed anThe samples were then exposed to 38 ppm, 3 ppm and0 ppm acetic acid vapors in separate Pyrex desiccators.

initial exponential rise in organic acid content inside theAfter a 14-day period of exposure, half of the samples

box that plateaued after roughly two months, for a shortperiod, before rising again as ambient temperature rosewith seasonal change (Figure 3). It was theorized that thewere analyzed by ion chromatography (IC) (MetrohmMetrosep A Supp. 5-250/4.0 column combined with 3.2
mmol/L of Na2CO3 + 1mmol/L of NaHCO3) for acetic

rapid organic acid build-up inside a “clean” storage box
made of allegedly low-emitting materials happened
because of the semi-airtight construction of the box,

acid adsorbed content. The other half was left to desorb
excess gas for 7 days in a controlled environment, andthen analyzed by IC to see retained acetic acid content

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6. Acidification of woodblock prints in an acetic

and calculate the off-gassed amount. Sample solutions
prepared for IC analysis were also measured for pH.

prints tendentiously have a heterogenous pH distribution
and areas with lower pH values would be more
vulnerable to pronounced acidification in storage, which
in turn, was found to moderately correlate to higher acidic
off-gassing.
The findings compiled so far call for the re-evaluationof the use of storage boxes with semi-tight construction
and for the development of mitigation strategies tocombat VOC build up in storage microclimates. Using theFFU system for routine cleansing or, even employing
traditional but forgotten practices like mushiboshi(periodical “airing” of stored artifacts) were suggested as

Figure 4. Retained and off-gassed conc. in samples, and pH value
before and after exposure to 3 ppm vapors of acetic acid (Des-Lo).

simple and innocuous mitigation strategies. Future
research should expand on these findings and examine thepotential damage in collections associated with

Obtained results suggest that diverging off-gassing
values in a multi-colored woodblock print may be
attributed to different pigment characteristics, and it does

VOC-concentrated microclimates in storage containers,
as well as explore practical solutions to combat this issue.

not necessarily correlate to degree of acidification. It wasalso shown that exposure to acetic acid-concentrated
environments contributed to heterogenous acidification ofReferences

woodblock prints. However, severe acidification incertain samples was associated with excess oxalic acidformation induced by exposure to high concentrations ofEstimation from VOC Emissions, Sensors 7 (12), pp.3136-3145, 2007

acetic acid that did not reflect normal storage conditions.
As such, results from laboratory experiments should beinterpreted carefully.

(1), pp.1-11, 2018

1) Strlič, Matija; Cigić, Irena K.; Kolar, Jana; De Bruin, Gerrit; Pihlar,Boris: Non-Destructive Evaluation of Historical Paper Based on pH2) Bembibre, Cecilia; Strlič, Matija: Smell of heritage: A framework for theidentification, analysis and archival of historic odours, Heritage Science 53) Mašková, Ludmila; Smolík, Jiří; Ďurovič, Michal: Characterization ofindoor air quality in different archives – Possible implications for booksand manuscripts. Building and Environment 7, pp.59-70, 2010

7. Conclusion
The research detailed in this dissertation showed that4) Gibson, Lorraine T.; Ewlad-Ahmed, Abdunaser; Knight, Barry ; Horie,

acidic off-gassing in woodblock prints is primarilyindicative of their storage environment. The storage oforganic compounds emitted in libraries and archives: an inferential

woodblock prints in closed boxes of semi-airtight5) Hughes, Amy; Keynan, Daria: Testing the Waters: New Technicalconstruction seemingly facilitates the creation of anApplications for the Cleaning of Acrylic Paint Films and Paper Supports,

organic acid-concentrated microclimate that may lead toVOC build up in center/inner areas of stored prints that

The Book and Paper Group Annual, pp.43-51, 2013

are further away from the openings of a container, wheremore severe acidification may occur. Estimating theRinshō Hozon = Clinical Conservation at the Tokyo National Museum,conservation risks of woodblock prints after long-term7) Carter, Henry; Bégin, Paul; Grattan, David: Migration of volatile

exposure to organic acid-concentrated microclimates innormal storage conditions is difficult as laboratory data islimited. It is, however, understood that some components

compounds through stacked sheets of paper during accelerated ageing-part

Velson; Mitchell, Gemma; Robertson, Claire J.: Measurement of volatile

indicator of paper decay?, Chemistry Central Journal 6 (1), p.42, 2012

6) Tokyo National Museum (ed): Tōkyō Kokuritsu Hakubutsukan noBijutsu Shuppansha. 2013

1, Restaurator 21 (2), pp.77-84, 2000of woodblock prints might make them some susceptible
to organic acid-induced degradation, such as areas withpH-sensitive pigments. It was also understood that these
Summaries of Academic Theses 2021