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Bull. Soc. Photogr. Imag. Japan. (2014) Vol. 24 No. 1: 6–11

Original Paper

Method for Increasing the Durability of Transcribed Gold-Layer Photographs
Ken’ichi Kuge* and Kenta Nojo*

Abstract:

Baking conditions for the preparation of gold-layer photographs via transcription on a porcelain base were investigated with theaim of increasing the durability of the photographs. It was found that increasing the maximum baking temperature increased the
durability of the gold layer against scratching. This increase, however, brought about a reddening of the image and a decrease in
the maximum optical reflection density. Images from the photographs that were baked above 900°C were retained even after
scratching the photograph with sandpaper or dissolution of the gold layer in a tincture of iodine. It is proposed that the glaze
layer on the porcelain base softened up after baking at temperatures above 800–900°C and that the gold layer gradually sank into
the glaze layer. At the same time, the boundary between the gold and glaze layers fused, increasing the adherence of the gold
layer to the glaze layer.

Key words:

Silver-salt photography, Image preservation, Photographic printing paper, Gold, Baking

1. Introduction
Photographs are created with the aim of preserving images sothat the images can be viewed later. The progress of photographic
technology has always been associated with problems in image
preservation. Recently, the development of digital photographic
system has given rise to a new problem of digital data preservation 1).
The fact that black-and-white photographs taken in the earlystages exist today has shown their high capability for preservation,and it is expected that the lifetime of these photographs is morethan 500 years 2) 3). However, as of now, it is not possible to preserve these photographs for extremely long periods of time, e.g.
beyond 1000 years, as is observed in the case of stone monuments
such as the Rosetta stone.
To address this problem, we developed the gold-deposition
development­ method 4)–10) and created a gold-layer photograph byaltering the image with gold particles deposited on a ceramic basethrough baking 11)–15). Because they consist of a gold layer and aceramic base, which are both chemically stable, these gold-layer
photographs are expected to be preserved for extremely long
periods­. Moreover, we developed a method for creating a transcribed gold-layer photograph by pasting printed paper with animage made of gold particles onto a heat-resistant base and baking
it 16). This method does not require the initial preparation of photographic materials with heat-resistant bases. Further, this method
also generates chemically stable photographs because these photographs consist of only a gold layer and a stable base.
The gold-layer photographs and the transcribed gold-layer
photographs prepared by the above-mentioned methods had adrawback, however: the adhesion of the gold layer to the base was

not strong enough, and the image could easily be damaged byscratching. Moreover, when such a gold-layer photograph is­immersed in water for long periods of time, the gold layer isgradually exfoliated from the base 17). Unless these shortcomings
are overcome, these photographs cannot be preserved for extremely
long time periods. In this study, we investigated the baking conditions used in preparing a transcribed gold-layer photograph on aporcelain base. The aim was to determine the conditions underwhich the gold layer would firmly adhere to the base, so thattranscribed gold-layer photographs with high durability can beproduced.

2. Experimental method
Baryta printing paper (Lodima Photo Paper) was used toprepare photographic images composed of gold particles*. Golddeposition was performed on the papers with either stepwise
exposure or uniform exposure. In the stepwise-exposure process,the area to be exposed was divided into several parts and the light
exposure for each part was increased in a stepwise fashion. The
conditions used for the gold-deposition development were the sameas reported previously 16). The formula for the development is shownin Table 1.
The printing papers were pasted on a base of white porcelain
tile by using 0.8–2% gelatin solution as an adhesive. Normally, weused the 0.8% solution, but we increased the concentration gradually to 2%, when a warp in the paper increased. The printed sideof the paper was kept in contact with the base. After baking in anelectric furnace, the paper base and the gelatin in the emulsion
layer burned out and the gold particles melted, thus a transcribed

Received 10th, September 2013; Accepted 8th, May 2014
*Graduate School of Advanced Integration Science, Chiba University, 1-33, Yayoi-cho, Inage-ku, Chiba 263-8522, Japan

Kuge and Nojo   Method for Increasing the Durability of Transcribed Gold-Layer Photographs

Table 1. Formula for gold deposition development
Reagent solution

Concentration

AmountSolution A
KSCN
NaAuCl4·2H 2O
KBr
Water to make

0.1 mol/L
0.05 mol/L
0.8 mol/L

40 mL
20 mL
10 mL
900 mL

0.1 mol/L

100 mL

Solution B
Ascorbic acid

The solutions A and B were mixed and immediately used for development.

gold-layer photograph was created. The temperature inside thefurnace was raised in two steps, as described previously 13). In thefirst step, the rate of temperature increase and final temperature
were 60°C/h and 420°C, respectively. This final temperature wasmaintained for 1 h before starting the second step. In the second
step, the rate of temperature increase was 120°C/h and the final
temperature varied from 700°C to 1100°C. The samples were allowed to cool down in the furnace after being held at the final
temperature for 3 h.
The durability against scratching of the gold layer on the photographs was evaluated by two methods. In the first method, thegold layer was rubbed 50 times with a wet, hard scourer by handat a constant power throughout**. In the second method, the gold
layer was scratched 50 times with sandpaper (No. 1500) with thesame procedure as the first method.
The durability of the images in water was evaluated as follows.
The photographs were immersed in warm water at 60°C for a­certain period of time. Their optical reflection density (OD) was
then measured, and then the gold layer was rubbed with a scourer
and the exfoliation of the gold layer was examined visually. The
durability of the images in other solutions, including acetic acid,sodium carbonate, and surfactant (Drywell, Fujifilm) solutions,were also evaluated by the same method. The ODs of the goldlayer photograph on the printing paper before baking and thetranscribed gold-layer photograph after baking were measured
with a densitometer (Model 2119, Abe Design). The reflection
spectra of the photographs were measured with a spectrophoto­
meter (UV-2550PC, Shimadzu).
The dissolution of the gold layer was examined by immersing
the photograph in a tincture of iodine, which can dissolve gold.
This iodine tincture was prepared by dissolving 6 g of iodine and
4 g of potassium iodide in a mixture of 70 mL ethanol and 30 mL
water.

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3. Experimental results
The photographic characteristic curves for the gold-particle
photographs on printing paper before baking and the transcribedgold-layer photographs after baking are shown in Fig. 1. The final
baking temperature was varied between 700°C and 900°C. The
maximum OD of the gold-layer photographs was lower thanthose of the images on the printing paper measured before baking. This decrease in the maximum values of ODs after baking
became notable as the baking temperature was increased. Moreover, this decrease in OD resulted in a reduction in the contrastof the photographs. The surface of glaze layer in areas without
gold layer coverage became rough after baking at 900°C or higher,
resulting in a decrease in surface luster.
Changes in OD of the transcribed gold-layer photographs
baked at 700–1100°C caused by rubbing with a scourer or scratching with sandpaper for 50 times are shown in Fig. 2. The higher
the baking temperature was, the lower the OD measured after
baking became. Thus, the largest decrease in OD was observed
for the sample baked at 1100°C. No significant decrease in OD
was observed after rubbing the baked photographs with a scourer.
On the other hand, the OD drastically decreased after scratchingwith the sandpaper for the samples baked at 700–750°C. In thiscase, the gold layer was removed upon scratching, revealing thewhite surface of the tile base. The decrease in OD due to sandpaper damage became smaller with increasing baking temperature.
The OD hardly changed for the sample baked at 1100°C, although the OD of this sample was already decreased significantly
due to the baking.
Images of the photograph surfaces observed with an optical
microscope are shown in Fig. 3. It can be seen that the gold layerof the photograph baked at 700°C was almost completely removed
down to the white surface of the tile base after scratching it withthe sandpaper. In contrast, a large part of gold layer still remained
and the area of white base was smaller for the sample baked at
800°C. The white base is not visible for the sample baked at
900°C and the gold layer remains on the all observed areas.
The ODs of the samples baked at 700–900°C observed after
various repetitions of sandpaper scratching are shown in Fig. 4.
The OD decreased more rapidly for the sample that was baked at
700°C than the sample baked at 800°C. Compared to these results, the OD for the sample baked at 900°C decreased only
slightly with increasing sandpaper scratching times. This tendency
is similar to the trend observed in Fig. 2.
The reflection spectra before and after scratching with sandpaper 50 times are shown in Fig. 5. Reflectance increased as baking
temperature rose. Relatively higher reflectance was observed in
the wavelengths region of longer than 550 nm. These spectral* When the printing paper of a resin coat (RC) is used, a thin layer of titanium oxide, which is included in the paper base 19), is formed upon baking. This
layer emits interference light, and the gold-layer image is hidden by this light. On the other hand, barium sulfate contained in the base of the baryta
printing paper 20) is in a powder form and is removed easily by baking.
** The loads applied upon rubbing or scratching were not measured because these treatments were carried out by hand. However, the same person always
carried out this process to ensure the same load was applied each time.

8Bull. Soc. Photogr. Imag. Japan. Vol. 24 No. 1 (2014)

Fig. 1. Photographic characteristic curves of transcribed gold-layer
photographs baked at different temperatures. The solid line
shows the curve for the printing paper before transcribing andbaking; the dashed lines are for after transcribing and baking.

Fig. 2. Changes in optical density of the transcribed gold-layer
photographs prepared at different baking temperatures caused byrubbing with a scourer or scratching with sandpaper for 50 times.

Fig. 3. Optical micrographs of the surface of transcribed gold-layer photographs. The gold-layer photographs were prepared at different baking
temperatures. The images on the left (a), center (b), and right (c) columns show the results before scratching with a sandpaper (a), after one-timescratching (b), and after 10-times scratching (c), respectively. The top (1), middle (2), and bottom (3) rows show the results for baking at 700, 800,
and 900°C, respectively.

Kuge and Nojo   Method for Increasing the Durability of Transcribed Gold-Layer Photographs

Fig. 4. Resistance of transcribed gold-layer photographs prepared at
different baking-temperatures to sandpaper scratching
represented as a change in optical density with sandpaperscratching times.

Fig. 5. Reflection spectra of transcribed gold-layer photographs baked at
different temperatures. Top: before scratching; bottom: after
sandpaper-scratching for 50 times.

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Fig. 6. Decrease in the optical density of transcribed gold-layer
photographs baked at different temperatures after immersion in
the tincture of iodine for different periods. The decrease isrepresented as the ratio of OD before and after immersion.

characteristics contributed to the decrease in overall OD for samples baked at higher temperatures. Scratching did not result in alarge change in the spectra, and therefore, the hue of photographs
did not change after scratching.
The results of the analysis of gold layer dissolution by the tincture of iodine are shown in Fig. 6. The tincture dissolves the gold
layer if any part of it is uncovered, and when that happens, thewhite surface of the tile base is revealed. However, if the gold
layer is covered with or buried under a protective layer, the immersion in the tincture will not cause any change to the gold
layer. Figure 6 shows the ratio of OD before and after immersion
versus the immersion period represented on a logarithmic scale.
The ratio of OD decreased with time immersed in the tincture ofiodine. The gold layer for the sample baked at 700°C almost disappeared after 20 minutes of immersion. For samples baked at
higher temperatures, the decrease in the OD ratio became smallerwith time and the gold layer was not completely removed.
The characteristic curve for the sample baked at 700°C and immersed for 5 months in warm water is shown in Fig. 7. The OD
did not significantly change after immersion in water for thissample. The gold layer on the transcribed photograph did not
exfoliate by immersion in pure water. This is contrary to the previous studies 17), in which the gold layer was exfoliated upon immersion in water for a gold-layer photograph prepared directly ona glass plate. Therefore, the method used to transcribe photographs in this study has increased the durability of gold-layer
against the immersion in water.
The results of durability of samples baked at different temperatures against the immersion in warm water for certain periods oftime are listed in Table 2. For samples baked at 700 and 750°C,

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Bull. Soc. Photogr. Imag. Japan. Vol. 24 No. 1 (2014)

Fig. 7. Photographic characteristic curves of transcribed gold-layer
photographs before and after immersion in water at 60°C for 5
months. The gold-layer photographs were baked at 700°C. Solidline: before immersion, dashed line: after immersion.
Table 2.

Exfoliation of gold-layer on the photographs by immersion ina water at 60°C for one day or half a year

Bakingtemperature/°C
700
750
800
850
900

Treatment
Immersing 1 day andrubbing with a finger
×
×
○
○
○

Immersing for a halfyear and rubbing witha scourer
—
—
△
○
○

×: exfoliation, —: no data△: decrease of density, ○: no change

after one day immersion in water, the gold layer was exfoliatedeven by soft rubbing with a finger. In contrast, the OD of thesamples baked at 850 or 900°C did not change by rubbing with ascourer even after immersion in water for half a year, although asmall decrease in OD was observed for the sample baked at
800°C. The immersion in the other solutions examined in thisstudy also showed similar results. It can be stated that hightemperature baking of transcribed gold-layer photographs resultsin the gold layer adhering strongly to the ceramic base.

4. Discussion
By increasing the baking temperature, resistance to both
scratching and immersion in water increased and the durability of
the gold layer was enhanced. Normally, porcelains consist of twoparts: a porous base and a glassy glaze layer covering the base. Thebase has high thermal stability, while the glaze layer softens up
and then melts above 800–900°C, as evidenced by the increase inroughness and decrease in luster of the surface of glaze layer.
However, the glaze layer does not have a definite melting point
owing to its glass-like properties.
The gold layer deposited on the glaze layer is not uniformly flat.

Fig. 8. Schematic diagram of the transcription process for preparing
gold-layer photographs, (a) before baking, (b) below 420°C in thefirst baking step with raising temperature of 60°C/h, (c) above
420°C in the second baking step with raising temperature of
120°C/h, (d) above 800°C after softening up and melting of theglaze layer.

The layer consists of aggregates of gold clusters, which are formed
upon sintering of the gold particles 12). The gold layer has highelectric conductivity, and hence the gold clusters are in contact
with each other through partial melting at the contact points.
The schematic diagram in Fig. 8 shows the assumed baking
process that leads to the formation of transcribed gold-layer photographs. This formation process helps us better understand themechanisms that lead to an improvement in the durability of thetranscribed gold-layer photographs. First, when the sample isbaked below 420°C, both the paper base and the gelatin in theemulsion layer are carbonized. Gold particles are dispersed in the
carbon layer as well. In the second baking process above 420°C,
the carbon layer gradually burns out completely. As the carbon
layer decreases in thickness, the gold particles come to contact
with each other and form clusters by sintering. Above about
700°C, the clusters melt and begin contacting each other to makea gold layer composed of the aggregates of clusters. At the sametime, the glaze layer begins to soften up and some gold clusters
sink into the glaze layer. The clusters that are not dissolved in theKuge and Nojo   Method for Increasing the Durability of Transcribed Gold-Layer Photographs

tincture of iodine increase with the increase in the number ofclusters buried in the glaze layer.
At temperatures above 800–900°C the gold layer sinks into theglaze layer and a part of it breaks up into gold clusters. These goldclusters are dispersed in the glaze layer and result in the red color
in the photographs, due to the plasmon absorption of the clusters.
This results in the increase in the stability of the gold layer orclusters against damage caused by scratching or dissolving. At thesame time, some gold atoms in the layer or clusters are gradually

dissolved into the glaze layer, because the liquid glaze is a solventof gold atoms 18). This dissolving increases with increasing baking
temperature. The dissolved atoms do not show any color and thisbrings about the decrease of OD that is seen for samples baked at
higher temperatures. If a layer of a solid solution of a high concentration of gold atoms in the glaze forms at the interface between the gold and the glaze layers, then the boundary between
these two layers becomes fuzzy. This lack of a clear boundary
between­the gold and the glaze layers is indicative of enhanced
adherence.

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