Elemental Analysis of Daguerreotype Chemistry Using the Orbis Micro-XRF Elemental Analyzer

Daguerreotype, named after its principal inventor Louis Jacque Mande Daguerre, was introduced by the French Academy of Sciences in 1839.

It was the first mainstream technique used for developing photographic images. In this method, a polished silver plate is used, which is subjected to a halogen-based fume so as to produce a light-sensitive surface for exposure.

When the plate is exposed to mercury fumes, ‘negative’ is developed. To reduce the black and white tone, a gold chloride solution is washed over the image to create a warmer amber hue or gilding.

Analysis of daguerreotypes for their elemental composition provides a better understanding about the history of first photochemistry, and may also reveal which chemicals were utilized during each step of the process.

Analysis of Daguerreotype Chemistry Using the Orbis Micro-XRF Elemental Analyzer

Micro X-ray fluorescence (micro-XRF) is a non-destructive, elemental analysis technique that uses an X-ray source to create typical signals from the sample. In this article, an EDAX Orbis PC equipped with a 50mm2 silicon drift detector along with a poly-capillary optic oriented normal to the sample was utilized. In addition, an XYZ stage and in-built video cameras enabled sample navigation of 100mm in each direction.

Since micro-XRF analysis is non-destructive and requires minimum sample preparation, it is suitable for these kinds of samples. Moreover, since no sample charging is associated with X-ray excitation, the sample need not be coated.

Given the fact that spot size of the Orbis is larger than that of the spot size of energy dispersive spectroscopy (EDS), micro-XRF is more suitable for larger areas and larger samples of interest. Figure 1 shows a part of a daguerreotype obtained by means of the Orbis PC internal low magnification 10X camera.

Approximately a 4 x 3mm video image capture of the daguerreotype. Note that the reflection left of center is from the X-ray optic, which is situated directly above the sample.

Figure 1. Approximately a 4 x 3mm video image capture of the daguerreotype. Note that the reflection left of center is from the X-ray optic, which is situated directly above the sample.

Although the overall chemistry of the plate was known, the Orbis Micro-XRF elemental analyzer was utilized to detect all unknown elements and their distribution, specifically, the elemental composition of the pink region depicted on the left cheek. It looks as if it has been added on purpose rather than discoloration. Again, completing this process sans destroying the sample is very important.

In order to obtain a spectral distribution map, the stage shifts in a 2D raster whilst the X-ray detector acquires a set of points, scaling the intensities for each element. For this sample, the running conditions were 40kV, 600uA on a rhodium-anode X-ray tube. The scan acquired 256 x 200 points in the X and Y directions with the 30µm poly-capillary, for 0.4 seconds for each point. Maps for gold (Au) with L-series on the right and M-series on the left are shown in Figure 2. The capacity to operate at higher energies with micro-XRF analyzer helps in making comparison of two transition sequence of the same element.

The (a) Au(M) and (b) Au(L) maps for comparison, with the M-series being more indicative of surface distribution.

Figure 2. The (a) Au(M) and (b) Au(L) maps for comparison, with the M-series being more indicative of surface distribution.

With the M-series lines being less energetic, the photons exhibit less escape potential, rendering more surface-sensitive data. The L-series with comparatively greater escape potential would be more indicative of sub-surface composition.

Figure 3 shows the Fe(K) map, in which a distinct streak of iron (Fe) is seen, which corresponds to the location of the pink hue in the video image. Here, Fe is evidently the main component, which is consistent with the prior methods of introducing color through materials such as copper or iron oxides.

Fe(K) map shows a streak consistent with the pink hue on the cheek.

Figure 3. Fe(K) map shows a streak consistent with the pink hue on the cheek.

Conclusion

A wide range of elements related to daguerreotypes were thus identified. Similar to gold and iron, each element confirmed which of the chemicals were utilized at each step of the process. Micro-XRF analysis allows nondestructive analysis and requires minimal sample preparation. Moreover, unlike an electron beam, the sampling area is more suitably covered by an X-ray beam. Since sensitivity is known to enhance with higher atomic numbers for micro-XRF, gold, iron and other heavier metals disclose more about the processes that go behind producing these early photographs.

About Edax Inc

EDAX is the global leader in Energy Dispersive X-ray Microanalysis, Electron Backscatter Diffraction and Micro X-ray Fluorescence systems. EDAX manufactures, markets and services high-quality products and systems for leading companies in semiconductors, metals, and geological, biological, material and ceramics markets.

Since its founding in 1962, EDAX has utilized its knowledge and expertise to develop ultra-sensitive silicon radiation sensors, digital electronics and specialized application software that facilitate solutions to research, development and industrial requirements.

EDAX is a unit of AMETEK Materials Analysis Division. AMETEK, Inc. is a leading global manufacturer of electronic instruments and electric motors with annualized sales of more than $1.8 billion.

This information has been sourced, reviewed and adapted from materials provided by Edax Inc.

For more information on this source, please visit EDAX Inc.

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