Microscopy and Analysis
This chapter includes description of a camera set-up for
The identification of several of the attributes of photographs
requires close examination under appropriate illumination and
with some degree of magnification. Following are some suggested
1) A hand magnifier and a pencil flashlight.
Hand magnifiers are available from magnifications of about 4x
to 20x. At lower magnifications the best illumination for
faithful color rendition is daylight. The higher powers require
more light, and because the working distance becomes quite
short, the light needs to be tightly focused. Grazing angle
lighting is useful in revealing layers such as in Woodburytypes
and carbon prints. Transmitted light can reveal paper fibers in
the highlight regions of unmounted salt prints and albumen
prints such as tissue stereos.
2) Close-focusing cameras
A camera equipped for macrophotography and mounted on a copy
stand can be a useful inspection tool as well as a recorder.
Many 35mm reflex cameras can be equipped with bellows focusing
attachments or with combinations of extension tubes. Some
asymmetrical lenses can be reversed with a mounting adapter to
give more magnification. The mounting stand should be rigid and
free of vibration, particularly for copying, because movement
of the mirror mechanism in reflex cameras during exposure can
blur the picture.
The following home-made setup has proven useful to this writer
in many cases:
A 35mm reflex camera with automatic exposure control was
equipped with 75 mm of extension tubes and a reversed 25 mm
f1.9 Kodak Cine Ektar lens (from a 16mm movie camera), mounted
on an enlarger column with laboratory clamps. The specimens are
laid on a laboratory scissors jack for focusing, and
illuminated with microscope lights. Automatic exposure control
makes it easy to take record shots. This combination gives a
magnification of 6x with excellent definition over the
Illumination can be with microscope lights or miniature halogen
lamps, being careful not to expose the specimen to excessive
time-intensity levels. It should be remembered that old
photographs are subject to fading, and that the damage is
cumulative. Many archival organizations do not permit copying
of original photographs on office copiers for this reason.
3) Binocular inspection microscopes.
These are designed for good working distances at magnifications
up to about 90x. They are mounted on swing arms that can reach
the center of large photographs, and some can mount cameras for
permanent records. They are useful general purpose laboratory
4) Biological microscopes.
It is seldom that magnification up to several hundred is
needed, but it is available with biological microscopes at the
expense of very shallow depth of field. It is possible to focus
down through the paper fibers into the embedded image of salt
prints. Biological microscopes are usually mounted on rigid
C-frames, which prevent access to centers of photographs as
large as cabinet cards. The optical heads can often be
transferred to other mounts for large area examination.
Chemical and Physical Analysis
Some of the attributes listed in Section 1 of Chapter 14 can be
identified by inspection, and this will often suffice. When
inspection leaves doubts, and when the value of the unknown
picture is high (historically or monetarily), there is a good
probability that modern analytical methods can find the answer.
Two case studies are discussed in Appendix I and II. The
discussion below is a resume of available techniques.
The photosensitive material and the binder are the attributes
most likely to require analysis for identification.
1. Binder Identification
The solvent tests described by Rempel  have already been
mentioned in Chapter 2. They are simple to perform, but they
are destructive; this disadvantage can be minimized by limiting
the test to a small area outside the actual image. Infrared
spectrophotometry is capable of identifying any of the organic
binders nondestructively. The difficulty is in adapting the
instrument to a specimen the size of a photograph, since
cutting off a corner may be even less acceptable than the
2. Identification of Photosensitive Material
The compositions of most surviving 19th century photosensitive
materials except diazo dyes were based on metals. Classical wet
chemistry can identify the metals, but only destructively. It
can be done on microscopic zones by the use of colorometric
spot tests such as those given in Feigel .
One of the most useful non‑destructive analytical methods
that is applicable to specimens the size of photographs is
x‑ray fluorescence analysis. There are several types of
instrumentation, depending on the means of excitation.
Basically they depend on exciting the specimen to emit its
characteristic x‑ray spectrum, then analyzing the
wavelength or energy distribution of the spectrum.
Scanning Electron Microscopy
The x‑ray spectrum can be excited by bombarding the
specimen with electrons whose energy is a few kilovolts.
Scanning electron microscopes (SEM) generate their magnified
images by electron bombardment, with the emission of both
secondary electrons and x‑ rays from the specimen. The
secondary electrons are used to form the topographical images;
the by‑product x‑rays can be analyzed to give the
composition. This kind of analysis has to be done in a vacuum,
an environment that may damage photographs except
all‑metal Daguerreotype plates. Specimen size that can be
accommodated in electron microscopes is limited to a few
inches. Appendix I describes a scanning electron microscope
analysis of a Daguerreotype.
Radiation‑Excited X‑ray Analysis
Of more general use is the x‑ray fluorescence technique,
whose application to the analysis of photographic emulsions and
papers was reported in 1983 by Enyeart et at . Excitation
is by gamma radiation from radioisotopes or by X‑rays
from vacuum tubes. The analysis has been shown not to damage
photographs or to leave any residual induced radioactivity in
the specimens. It is safe, portable, non‑destructive, and
can be used on any size specimen. It will detect any of the
sensitizing elements in photographs except organic dyes. It
cannot distinguish between gelatin, collodion, and albumen
except indirectly by their impurity content. For example,
albumen contains detectable sulfur, and collodion may contain a
variety of preservatives as mentioned in Chapter 7. The
instrumentation is widely used in forensic and medical analysis
as well as numerous industrial applications; it has figured
prominently in the authentication of many art objects.
Cost and Availability
Scanning electron microscopes, X‑ray fluorescence,
infrared and ultraviolet spectrophotometers are beyond the
reach of most individuals for their capital cost as well as for
the necessary professional operators. But there are thousands
of such instruments in industrial and college laboratories, and
in consulting scientific laboratories where analyses can be
performed for a reasonable fee. There have even been instances
where graduate students or friends have been persuaded to
donate a noon hour or weekend for the analysis of a specimen of
The purpose of this discussion is to call attention to the
existence of appropriate analytical technology to archivists
and advanced collectors. For additional information, college
libraries have textbooks on the above‑mentioned
instruments, and the technical periodicals listed in Chapter 12
regularly contain relevant research papers.