Vol.3, No.11, 948-954 (2011) Natural Science
http://dx.doi.org/10.4236/ns.2011.311121
Photobleaching characteristics of traditional Japanese
paper in a museum environment
Kosuke Nakagoshi, Kunio Yoshizumi*
Kyoritsu Women’s University, Tokyo, Japan;
*Corresponding Author:
Received 16 September 2011; revised 22 October 2011; accepted October 29, 2011.
ABSTRACT
Photobleaching of aged traditional Japanese
paper that has been thermally yellowed during
storage for 200 years was examined from the
standpoint of accumulated light radiation dos-
age in a museum environment. The light inten-
sity was evaluated using a blue wool reference
of the Japan Industrial Standards (JIS) as a do-
simeter. The wavelength sensitivity of the pho-
tobleaching was compiled under monochro-
matic light radiation. Color changes in the spe-
cimens were measured in tristimuli values in
color. by using a color analyzer. The aged pieces
of paper were monitored continuously as they
were photobleached under three different light-
ing conditions in a museum environment for
8000 h. The combination of the yellowness in-
dex changes of the aged pieces of paper and the
color changes of a blue wool reference was in-
terpreted as follows. Photobleaching was gov-
erned by accumulated light intensities and was
independant upon daily lighting conditions. The
wavelength sensitivity of the photobleaching of
aged paper showed that the maximum effect
occurred at 420 nm in the visible light range.
The blue wool reference was confirmed to per-
form well as a dosimeter.
Keywords: Traditional Japanese Paper;
Photobleaching; Wavelength Sensitivity;
Monochromatic Light; Visible Light; Blue Wool
Reference; Dosimeter
1. INTRODUCTION
Since ancient time, human has used many types of
paper, each with its own history. However, the basic
characteristics of all these papers may be considered to
be derived from lignocellulosic materials [1]. Their du-
rability with respect to photochemistry has been the
subject of numerous studies [2]. However, further work
is still required for a detailed understanding of photode-
gradation processes [3-5]. The materials from which
paper is made consist of not a simple component but
complicated compounds. Therefore, a comprehensive
examination of this subject should be useful from the
standpoint of natural sciences.
The paper containing lignin has a light-brown ap-
pearance. Lignin is a cross-linked racemic macromolecule
with a molecular mass in excess of 10,000 u. It is rela-
tively hydrophobic and aromatic in nature. The degree of
polymerization in nature is difficult to measure as it is
fragmented during extraction and its molecules consist
of various substructures that appear to repeat themselves
in a haphazard manner [6]. White paper is required for
many end uses and therefore the paper containing lignin
is chemically bleached [1]. Yellowing occurs as a result
of thermal and photochemical reactions [7-9].
The natural phenomenon of photobleaching was ob-
served in early times and used to whiten paper and tex-
tiles [10-14]. Sun-bleached paper found first mention in
a compilation of recipes dating back to the 17th century,
in which it was suggested that prints could be bleached
by exposing them to sunlight while wet [11].
In this study, photobleaching of traditional Japanese
paper was examined in a museum environment. Few
studies have been conducted on the characteristics of the
degradation of traditional Japanese paper. The specimen
used in this study had already yellowed as a result of a
slow but prolonged thermal reaction [10] caused by
long-time storage for about 200 years.
This study consists of three experimental keypoints:
First, continuous monitoring of the photobleaching of
the specimen was conducted under different lighting
levels in a museum for 8000 h. Second, the light inten-
sity was simultaneously monitored by using a blue wool
reference as a dosimeter. Third, the above data were
combined to interpret them consistently with a CIE color-
change scale.

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954
949949
In addition, the wavelength sensitivity of the photo-
bleaching of the specimen was investigated to character-
ize the nature of the photobleaching in comparison with
previous studies with respect to protein-containing wool
and silk substances [15-19].
The information collected in this study on the charac-
teristics of color change in traditional Japanese paper in
a museum environment will prove useful in the conser-
vation of traditional cultural properties.
2. EXPERIMENTAL
2.1. Materials
2.1.1. Traditional Japanese Paper
The specimen used in this study was taken from an
accounting ledger of about 300 pages. The date of 1809,
which was during the Edo Era of the Tokugawa Shogun,
was written in India ink using a brush on the front cover.
Thus, we assume that the paper was made about 200
years ago in Japan. The surface was thermally yellowed
in color (X = 64.1, Y = 67.6, Z = 50.0; yellowness index
= 38.8, n = 7). The paper fiber was made of wood—
paper mulberry, kozo, and mitsumata—which were tra-
ditional materials used to make paper during the Edo Era.
The weight of the paper was 35.04 g/m2.
2.1.2. Use of Standard Dyed Cloth as Dosimeter
A blue wool reference of the Japan Industrial Stan-
dards (JIS) [20] for evaluating colorfastness under day-
light was used as a dosimeter to monitor light intensity
in a museum [21]. The first grade standard was selected
because it is the most fugitive, being dyed with C. I.
Acid Blue 104 on a wool substrate. The blue wool stan-
dards consist of a set of wool samples that progressively
and irreversibly fade when exposed to light. The speci-
mens are loaded with different light-sensitive blue dyes
so as to present different rates of fading. In principle, the
JIS blue wool standard is similar to the ISO blue wool
standard [22].
2.2. Exposure to Light Sources
2.2.1. Polychromatic Light in a Museum
The lighting conditions in three rooms—two exhibi-
tion rooms and a storage room—in a museum environ-
ment in Ishikawa Prefecture, Japan were examined in
this study. The lighting was commonly provided by
halogen lamps (Iwasaki, type JD110), which irradiate a
stronger light under a given wattage and a whiter light
compared to an ordinary light bulb with a tungsten fila-
ment. Exhibition room A was lit at the brightest level
because details of the objects on display had to be
clearly visible to visitors. The lighting in exhibition
room B was kept at a lower level because the objects on
display were more sensitive to deterioration under bright
lighting conditions. The lights in the storage room were
usually turned off other than when checking stored ob-
jects, which occurred rarely.
The exposure experiments were conducted through
February 2, 2007 and January 17, 2008. Total exposure
time was 8000 hours.
2.2.2. Monochromatic Light in a Laboratory
The samples were irradiated with monochromatic light
by using a JASCO CRM-FD spectroirradiator (Figure 1).
The spectroirradiator was equipped with a 300 W Xe arc
lamp with an elliptical half-sphere mirror to collect light
emission. Radiation from this source was converted into
monochromatic light by using a diffraction lattice grat-
ing with 1200 lines/mm. The wavelength dispersion was
about 2 nm·mm−1 and the slit was set to 2 mm, resulting
in an accuracy of about 4 nm for each irradiation wave-
length. The specimens were placed in an appropriate
position in a sample holder and exposed to monochro-
matic radiations interspaced by about 16 nm within the
208 - 650 nm wavelength range. The light intensity in
W/m2/nm was periodically measured for each wave-
length by using a photometer. The photometer was an
advanced device that consisted of a thermopile detector
attached to the spectroirradiator. Light exposures were
carried out at temperatures and relative humidities rang-
ing from 20˚C to 25˚C and from 50% to 70%, respectively.
These systems were used in previous experiments
published elsewhere [23,24].
2.2.3. Polychromatic Light in a Laboratory
Specimens were also exposed to polychromatic light
using an Atlas CI 35 xenon-arc Fade-O-meter, during
which a radiant energy of 1.1 W/m2/nm at 420 nm was
1
2
3
4
6
7
8
9
5
Figure 1. Schematic diagram of spec-
tro-irradiator: 1: Xenon arc lamp; 2:
Elliptical sphere mirror; 3: Mirror; 4:
Slit; 5: Mirror; 6: Mirror; 7: Diffraction
grating; 8: Mirror; 9: Sample holder.

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954 950
maintained.
2.3. Evaluation of Fading Characteristics
The specimen color change was measured using a
Minolta Model CM-3700d color analyzer with a 4  7
mm2 viewing aperture. Color indices were expressed in
XYZ and L*a*b* systems.
The amount of fading was evaluated in terms of yel-
lowness index and color difference as follows:

YI1.316X1.164ZY 100 
where X, Y and Z are tristimuli values in color.
And moreover, color difference was evaluated as fol-
lows:

12
222
EL*a*b*

 

,
where ΔL* is the lightness-darkness difference, Δa* is
the redness-greenness difference, and Δb* is the yel-
lowness-blueness difference.
2.4. Determination of Radiant Wavelength
Sensitivity
The accumulated energy (J/m2/nm) was calculated in
light intensity (W/m2/nm) by exposure time for each
exposure wavelength, because the light source did not
radiate at the same intensity at each wavelength. For a
specimen, the relationship between the accumulated ra-
diant energy and the yellowness index difference was
examined in a time sequential experiment at each expo-
sure wavelength. Then, a smooth curve was drawn to
give a representative fading characteristic. Yellowness
index difference data under a specified radiant energy
was read out from the curve to obtain wavelength sensi-
tivity characteristics at each exposure wavelength.
3. RESULTS AND DISCUSSION
3.1. Color Change in Traditional Japanese
Paper in a Museum Environment
Figure 2 shows the photobleaching characteristics of
traditional Japanese yellowed paper in a museum envi-
ronment.
Before the discussion on photobleaching, we will
present here a brief review on yellowness. The origin of
the coloring materials in the paper containing lignin is
lignin. The tendency of paper to yellow, called bright-
ness reversion, occurs through the following two
mechanisms: The first one is thermal, oxidative discol-
oration resulting from prolonged storage at ambient
temperature. Thermal reversion is dependant upon tem-
perature and humidity. The second one is photochemical,
-15
-12
-9
-6
-3
0
02000 4000 6000 8000
：Exhibition room A
■：Exhibition room B
●：Storage room
Exposure tim
e
i
n
the museum environment,hr
Yello
w
nessIndex dif
f
erence, ΔYI
Figure 2. Photobleaching characteristics of traditional Japa-
nese yellowed paper in a museum environment.
oxidative discoloration of paper through exposure to
daylight. Photochemical reversion or light-induced yel-
lowing of paper occurs within a short period [16]. It is
considered that both thermal yellowing and light-in-
duced yellowing are attributable to changes in lignin—
the formation of complicated lignin derivatives—which
are not easily identified [9]. Some aged paper may have
chromophores, which result from the presence of lignin
and also stem from the degradation of the cellulosic
fraction [11].
As shown in Figure 2, thermally yellowed specimens
were observed to be photobleached. The changing levels
are indicated as a yellowness index difference. The yel-
lowness decreased noticeably according to the exposure
time in a museum environment. Moreover, the extent of
yellowness change seems to depend upon the lighting
conditions. In exhibition room A, where the light was
the brightest, the degree of yellowness changed the
most—to a yellowness index difference of about 13 after
8000 h of exposure. The next obvious change was ob-
served in exhibition room B, where the light was main-
tained at a lower level. There, the yellowness index dif-
ference was limited to about 7.5 after about 8000 h ex-
posure. The minimum level was observed in the storage
room, where the lights were usually off, at a yellowness
index difference of about 3 for the duration of 8000 h. In
conclusion, the brighter the lighting conditions, the greater
the extent of bleaching of the yellowed paper.
The above results partly support the experiments
conducted by Annis and Reagan [10]. They examined

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954
951951
the photobleaching effect on a specimen from a 19th
century women’s yellowed nightgown that was naturally
aged cotton. The specimen was exposed to natural sun-
light in Kansas, USA, between 10 a.m. and 2 p.m. during
May and June for a total of 32 h. Annis and Reagan con-
cluded that the whiteness caused by hydrogen peroxide
bleaching and that caused by sun bleaching were com-
parable. With respect to the fact that aged yellowness
could be recovered, both our result and that of Annis and
Reagan share a common recognition.
3.2. Color Change in a Standard Dyed
Specimen in a Museum Environment
Figure 3 shows the fading characteristics of JIS blue
wool first grade lightfastness in a museum environment.
The light intensity in our study was expected to cause a
color change in the dyed reference. Moreover, it was
assumed that the same accumulated light intensity would
cause the same color change, as shown as a color differ-
ence based on the L*a*b* system during 8000 h of ex-
posure. As already discussed, rooms with three different
lighting levels were used in this study.
The maximum distinguishable color change was ob-
served to be about 11.5 of color difference in exhibition
room A, where the lighting was the strongest. The sec-
ond was observed to be about 7.0 of color difference in
exhibition room B. The third level was observed in the
0
3
6
9
12
15
02000 4000 6000 8000
：Exhibition room A
■：Exhibition room B
●：Storage room
Exposuretimein the museum environment,hr
Color difference, ΔE
Figure 3. Fading characteristics of JIS blue wool first grade
lightfastness standard in a museum environment.
storage room at about 2.5 of color difference. The order
of color change in the blue wool reference was similar to
that observed with respect to the yellowness index dif-
ference change.
3.3. Characteristics of Color Change in
Traditional Japanese Paper with
Respect to Dosimetry in a Museum
Environment
Figure 4 shows a comparison of the photobleaching
characteristics of traditional Japanese yellowed paper
and the fading characteristics of the JIS blue wool first
grade lightfastness standard in the same museum envi-
ronment. Figures 2 and 3 were combined into one figure
through common exposure times in different rooms, as
discussed above.
We obtained one cohesive line consisting of three dif-
ferent but overlapping lines observed under different
lighting conditions. That is, the same color difference in
the blue wool reference causes the same degree of
photobleaching and yellowness index difference of an
aged paper—irrespective of the lighting conditions. In
fact, the role of the dosimeter was fulfilled by a blue
wool reference in which color change occurred as ex-
pected.
In other words, it was verified that photobleaching
was controlled in a regular manner by photoradiation.
Thus, we submit a quantifying evidence that a lower
-15
-10
-5
0
0
：Exhibition room A
：Exhibition room B
●：Storage room
51015
Color difference,
Δ
E
Yello
w
ness Inde
x
diff er e nc
e
,ΔYI
Figure 4. Comparison of photobleaching characteristics of
traditional Japanese yellowed paper and fading characteristics
of JIS blue wool first grade lightfastness standard in the same
museum environment.

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954 952
accumulated light intensity causes less photodegradation
in general.
3.4. Reciprocal Relationship of Fading
Characteristics of Blue Wool
Reference
In the discussion on the characteristics shown in Fig-
ure 4, we assumed latently that the blue wool reference
would present the same color change—dependant solely
on accumulated light intensity and not on spasmodic
weak or strong light intensities—which is known as a
reciprocal relationship. We examined this assumption in
the experimental results shown in Figures 5 and 6.
First, the fading characteristics of the blue wool ref-
erence were examined as shown in Figure 5 under dif-
ferent radiation energies by using a fade-o-meter. Fol-
lowing three radiation conditions were set: 0.53, 0.70,
and 0.90 W/m2/nm at 420 nm. Different curves of color
difference were obtained for each radiation energy ac-
cording to the exposure time.
Next, the actual exposure time of the fade-o-meter
was converted into assumed exposure time in daylight
intensity, which is reported as an example of a represen-
tative fine day [25]. This is shown in Figure 6, which
shows a monotonous line that does not depend on the
radiation energy levels of the fade-o-meter. We conclude
that a reciprocal relationship is valid, albeit under lim-
ited radiation conditions.
3.5. Wavelength Sensitivity Characteristics
of Photobleaching of Traditional
Japanese Yellowed Paper
Figures 7(a) and (b) shows the fading characteristics
of traditional Japanese yellowed paper under 310 and
420 nm wavelengths of monochromatic light irradiation,
respectively. These wavelengths were selected as repre-
sentative to concisely observe the overall fading charac-
teristics. Each curve shows a variation in the yellowness
of the specimen under a continuous monochromatic ra-
diation at a constant wavelength. In this study, the yel-
lowness changing characteristics of the paper were com-
piled when the accumulated radiant energy reached 5
MJ/m2/nm for each wavelength. The final combined
form of the characteristics, also known as an action
spectrum [26,27], is shown in Figure 8. The photo-
bleaching-causing peak ranged between 250 and 530 nm,
as shown in Figure 8. The maximum peak was observed
at 420 nm in the visible light range. This suggests that
ultraviolet A-rays (UVA) and visible light radiation have
significant bleaching effects.
These experimental results of traditional Japanese
yellowed paper are consistent with previous studies as
0
3
6
9
12
15
050100 150 200 250 300 350
●
◆
■
Color difference, ΔE
Exposuretime,min
:0.90 W/m
2
/nm
:0.70 W/m
2
/nm
:0.53 W/m
2
/nm
Figure 5. Fading characteristics of JIS blue wool first grade
lightfastness standard, under energy intensities of 0.53 W/m2/nm,
0.70 W/m2/nm, and 0.90 W/m2/nm at 420 nm determined using
a fade-o-meter.
0
3
6
9
12
15
050100 150 200
◆
:1/2.2 Daylight intensity
:1/1.7 Daylightintensity
:1/1.3 Daylightintensity
■
●
Exposure time under simulated daylight, min
Color difference, ΔE
Figure 6. Fading characteristics of JIS blue wool first grade
lightfastness standard under simulated daylight radiation.
follows:
The maximum effect of photobleaching of mechanical
pulp paper was observed at 420 - 430 nm, although con-
siderable variations were found depending upon the tree
species [17].
In the 1970s, light bleaching of aged paper saw a re-
emergence in the United States, and equipment was
available on a commercial basis by the middle of the
1990s. Through methodological arguments, the effect of
UV versus visible radiation was brought to the attention
of researchers, leading to the recommendation that UV

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954
953953
-15
-12
-9
-6
-3
0
0100 200 300 400 500 600 700 800
a
-15
-12
-9
-6
-3
0
0 100200300400500600700800
b
Yello
w
ness Inde
x
dif
f
erence,
Δ
YIYello
w
ness Inde
x
dif
f
erence,
Δ
YI
Irradiation energy,MJ/m/nm
2
Irradiation energy,MJ/m/nm
2
Figure 7. Photobleaching characteristics of traditional Japa-
nese yellowed paper under (a) 310 nm and (b) 420 nm of
monochromatic light irradiation.
-12
-9
-6
-3
0
0100 200 300 400 500 600
Yellowness Indexdifference,ΔYI
Radiant wavelength, nm
Figure 8. Wavelength sensitivity characteristics for photo-
bleaching of traditional Japanese yellowed paper under 500
kJ/m2/nm at each wavelength.
be eliminated from use in paper exposure to a light
source [11]. This means that visible light is sufficiently
effective in bleaching aged paper.
Another field of chemistry is the photoaging of pro-
teins, which leads to photo yellowing. It is well known
that blue-light radiation is effective in bleaching yel-
lowed wool and silk fabrics [18,19].
Although the details of species derived from lignin
derivatives or protein compounds have not been well
characterized in terms of chemical structure analysis,
exposure to light at a wavelength greater than 400 nm
commonly destroys the long-wavelength emitting sub-
stances that are the origins of yellowing.
In this study, the chemical process of photobleaching
of aged paper has not been discussed sufficiently. How-
ever, we provide an interpretation [11] as below: Sun
bleaching of traditional textile and paper is related to the
modern-day pulp-bleaching processes that employ oxy-
gen, ozone, or hydrogen peroxide. These chemical ag-
ents work with the same species that, under solar radia-
tion exposure, are produced in the presence of air and
water. In the very minor quantities that are formed in
this manner, they contribute to the bleaching effect. Al-
though light bleaching of paper does not require the ap-
plication of a chemical, it too is a chemical intervention.
4. CONCLUSIONS
In this study, the photobleaching characteristics of
aged paper that was estimated to have been traditionally
made during the Edo Era were examined from the
viewpoints of radiation energy consistency and wave-
length dependency.
The following results were obtained:
1) Yellowed specimens were observed to be photo-
bleached according to the exposure time in a museum
environment. The extent of yellowness change seemed
to depend on the lighting intensities.
2) The combination of yellowness index changes and
color changes in a blue wool reference showed that the
yellowness index changes were controlled by accumu-
lated light intensities and were not dependant upon
lighting conditions, that is, brightness or darkness.
3) The use of the JIS blue wool reference as a do-
simeter was found to be valid.
4) The wavelength sensitivity characteristics of the
photobleaching of aged paper were compiled to show
that the maximum effect was observed at 420 nm in the
visible light range.
In conclusion, this study provides experimental evi-
dence that a lower accumulated light intensity causes
correspondingly less photobleaching with respect to
aged Japanese paper.
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