Photobleaching characteristics of traditional Japanese paper in a museum environment

doi:10.4236/ns.2011.311121

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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: [email protected]

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

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:



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

02000 4000 6000 8000

：Exhibition room A

■：Exhibition room B

●：Storage room

Exposure tim

the museum environment,hr

Yello

nessIndex dif

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

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

：Exhibition room A

：Exhibition room B

●：Storage room

51015

Color difference,

Yello

ness Inde

diff er e nc

,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

050100 150 200 250 300 350

●

◆

■

Color difference, ΔE

Exposuretime,min

:0.90 W/m

/nm

:0.70 W/m

/nm

:0.53 W/m

/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.

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

0100 200 300 400 500 600 700 800

-15

-12

-9

-6

-3

0 100200300400500600700800

Yello

ness Inde

dif

erence,

YIYello

ness Inde

dif

erence,

Irradiation energy,MJ/m/nm

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

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.

REFERENCES

[1] Kennedy, J.F., Phillips, G.O. and Williams, P.A. (1989)

Wood processing and utilization. Ellis Horwood Ltd.,

Chichester.

[2] Heitner, C. and Scaiano, J.C. (1993) Photochemical of

lignocelluosic materials. ASC Symposium Series 531,

New York.

[3] Earp, A.A., Rawling, T., Franklin, J.B. and Smith, G.B.

K. Nakagoshi et al. / Natural Science 3 (2011) 948-954

954

(2010) Perylene dye photodegradation due to ketones and

singlet oxygen. Dyes and Pigments, 84, 59-61.

doi:10.1016/j.dyepig.2009.06.012

[4] Sharratt, V., Hill, C.A.S., Zaihan J. and Kint, D.P.R.

(2011) The influence of photodegradation and weather-

ing on the water vapour sorption kinetic behaviour of

scots pine earlywood and latewood. Polymer Degrada-

tion and Stability, 96, 1210-1218.

doi:10.1016/j.polymdegradstab.2011.04.016

[5] Caupos, E., Mazellier P. and Croue, J.-P. (2011) Photo-

degradation of estrone enhanced by dissolved organic

matter under simulated sunlight. Water Research, 45,

3341-3350. doi:10.1016/j.watres.2011.03.047

[6] Wikipedia (2011) Lignin.

http://en.wikipedia.org/wiki/Lignin

[7] Nolan, P., Van den Akker, J.A. and Wink, W.A. (1945)

The fading of groundwood by light. Paper Trade Journal,

121, 33-37.

[8] Van den Akker, J.A., Lewis, H.F., Jones, G.W. and Bu-

chanan, M.A. (1949) The nature of the color changes in

groundwood. Tappi, 32, 187-192.

[9] Leary, G.J. (1967) The yellowing of wood by light. Tappi,

50, 17-19.

[10] Annis, Z.K. and Reagan B.M. (1979) Evaluation of se-

lected bleaching treatments suitable for historic white

cotton. Studies in Conservation, 24, 171-178.

doi:10.2307/1505779

[11] Brückle, I. (2009) Bleaching in paper production versus

conservation. Restaurator-International Journal for the

Preservation of Library and Archival Material, 30, 280-

293.

[12] Suess, H.U. (2009) Bleaching. Restaurator-International

Journal for the Preservation of Library and Archival

Material, 30, 245-279.

[13] Brückle, I. (2009) Bleaching paper in conservation: De-

cision-making parameters. Restaurator-International Jour-

nal for the Preservation of Library and Archival Material,

30, 321-332.

[14] Henniges, U. and Potthast, A. (2009) Bleaching revisited:

Impact of oxidative and reductive bleaching treatments

on cellulose and paper. Restaurator-International Jour-

nal for the Preservation of Library and Archival Material,

30, 294-320.

[15] Oye, R. (1989) Degradation of bookpaper. In: Kennedy,

J.F., Phillips, G.O. and Williams, P.A., Eds., Wood Proc-

essing and Utilization, Ellis Horwood Ltd., Chichester,

49.

[16] Heitner, H. (1993) Light-induced yellowing of wood-

containing papers. In: Heitner, C. and Scaiano, J.C. Eds.,

Photochemical of Lignocelluosic Materials, ASC Sympo-

sium Series 531, 1, 2-25.

[17] Forsskahl, I. and Tylli, H. (1993) Action spectra in the

UV and visible region of light-induced changes of vari-

ous refiner pulps. In: Heitner, C. and Scaiano, J.C. Eds.,

Photochemical of Lignocelluosic Materials, ASC Sympo-

sium Series 531, 3, 45-59.

[18] Takamura, E., Yoshizumi, K. and Crews, P.C. (2000)

Photo yellowing and photo bleaching of silk and wool

fabrics under monochromatic and multichromatic light

radiation. The Textile Specialty Group Postprints, American

Institute for Conservation of Historic & Artistic Works,

515, 75-81.

[19] Zhang, H., Cookson, P. and Wang, X. (2009) Compara-

tive study on accelerated weathering tests of wool fabrics.

Textiles Research Journal, 78, 1004-1010.

doi:10.1177/0040517507087857

[20] Japan Industrial Standard (1998) Test methods for color

fastness to daylight. L 0841.

[21] Mignani, A.G., Bacci, M., Mencaglia, A.A. and Senesi, F.

(2003) Equivalent light dosimetry in museums with blue

wool standards and optical fibers. IEEE Sensors Journal,

3, 108-114. doi:10.1109/JSEN.2003.809439

[22] ISO (1980) Textiles-test for colour fastness daylight.

105-B01.

[23] Imaizumi, A. and Yoshizumi, K. (2006) Effect of sub-

strates on action spectra of fading of a selected disperse

dyestuff under light radiation. Textile Research Journal,

76, 757-764. doi:10.1177/0040517506070056

[24] Imaizumi, A. and Yoshizumi, K. (2006) Fading charac-

teristics of a disperse dye on cellulose triacetate, polyes-

ter and nylon fabric substrates under monochromatic

light radiation. Coloration Technology, 122, 86-92.

doi:10.1111/j.1478-4408.2006.00014.x

[25] Japan Industrial Standard (1998) Secondary reference

crystalline solar cells. C 9811.

[26] CIE (International Commission on Illumination) (1987)

A reference action spectrum for ultraviolet induced ery-

thema in human skin. International Commission on Illu-

mination Journal, 6, 17-22.

[27] Andrady, A.L., Song, Y., Parthasarathy, V.R., Fuki, K.

and Torikai, A. (1991) Photoyellowing of mechanical

pulp, Part 1: Examination the wavelength sensitivity of

light-induced yellowing using monochromatic radiation.

Tappi Journal, 74, 162-168.