ASTM E883-11(2024)

Standard Guide for Reflected–Light Photomicrography

SIGNIFICANCE AND USE
4.1 This guide is useful for the photomicrography and photomacrography of metals and other materials.  
4.2 The subsequent processing of the photographic materials is also treated.
SCOPE
1.1 This guide outlines various methods which may be followed in the photography of metals and materials with the reflected-light microscope. Methods are included for preparation of prints and transparencies in black-and-white and in color, using both direct rapid and wet processes.  
1.2 Guidelines are suggested to yield photomicrographs of typical subjects and, to the extent possible, of atypical subjects as well. Information is included concerning techniques for the enhanced display of specific material features. Descriptive material is provided where necessary to clarify procedures. References are cited where detailed descriptions may be helpful.  
1.3 The sections appear in the following order:    
Referenced documents  
2  
Terminology  
3  
Significance and use  
4  
Magnification  
5  
Reproduction of photomicrographs  
6  
Optical systems  
7  
Illumination sources  
8  
Illumination of specimens  
9  
Focusing  
10  
Filters for photomicrography  
11  
Illumination techniques  
12  
Instant-processing films  
13  
Photographic materials  
14  
Photographic exposure  
15  
Photographic processing  
16  
Keywords  
17  
Suggestions for visual use of metallographic microscopes  
Appendix X1  
Guide for metallographic photomacrography  
Appendix X2  
Electronic photography  
Appendix X3  
1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use. Specific precautionary statements are given in X1.7.  
1.5 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Mar-2024
• ICS: 37.080 - Document imaging applications
• Technical Committee: E04 - Metallography
• Drafting Committee: E04.03 - Light Microscopy

Relations

• Replaces: ASTM E883-11(2017) - Standard Guide for Reflected–Light Photomicrography
• Effective Date: 01-Apr-2024
• Referred By: ASTM C1721-22 - Standard Guide for Petrographic Examination of Dimension Stone
• Effective Date: 01-Apr-2024
• Referred By: ASTM C295/C295M-19 - Standard Guide for Petrographic Examination of Aggregates for Concrete
• Effective Date: 01-Apr-2024
• Referred By: ASTM B577-19 - Standard Test Methods for Detection of Cuprous Oxide (Hydrogen Embrittlement Susceptibility) in Copper
• Effective Date: 01-Apr-2024
• Referred By: ASTM E2014-17 - Standard Guide on Metallographic Laboratory Safety
• Effective Date: 01-Apr-2024
• Referred By: ASTM D807-18 - Standard Practice for Assessing the Tendency of Industrial Boiler Waters to Cause Embrittlement (USBM Embrittlement Detector Method)
• Effective Date: 01-Apr-2024
• Referred By: ASTM E1268-19 - Standard Practice for Assessing the Degree of Banding or Orientation of Microstructures
• Effective Date: 01-Apr-2024
• Referred By: ASTM E235/E235M-23 - Standard Specification for Type K and Type N Mineral-Insulated, Metal-Sheathed Thermocouples for Nuclear or for Other High-Reliability Applications
• Effective Date: 01-Apr-2024
• Referred By: ASTM C856/C856M-20 - Standard Practice for Petrographic Examination of Hardened Concrete
• Effective Date: 01-Apr-2024
• Referred By: ASTM E768-99(2018) - Standard Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• Effective Date: 01-Apr-2024
• Referred By: ASTM E112-13(2021) - Standard Test Methods for Determining Average Grain Size
• Effective Date: 01-Apr-2024
• Referred By: ASTM F561-19 - Standard Practice for Retrieval and Analysis of Medical Devices, and Associated Tissues and Fluids
• Effective Date: 01-Apr-2024
• Referred By: ASTM E1382-97(2023) - Standard Test Methods for Determining Average Grain Size Using Semiautomatic and Automatic Image Analysis
• Effective Date: 01-Apr-2024
• Referred By: ASTM E1181-02(2023) - Standard Test Methods for Characterizing Duplex Grain Sizes
• Effective Date: 01-Apr-2024
• Referred By: ASTM F1854-15 - Standard Test Method for Stereological Evaluation of Porous Coatings on Medical Implants (Withdrawn 2024)
• Effective Date: 01-Apr-2024

Overview

ASTM E883-11(2024), titled Standard Guide for Reflected–Light Photomicrography, is a key international standard published by ASTM International. This guide provides comprehensive methods and best practices for the photography of metals and a range of materials using reflected-light microscopes. Suitable for both black-and-white and color imaging, it addresses traditional wet processes as well as rapid, direct imaging techniques, with considerations for both photomicrography and photomacrography. The standard also covers the critical post-processing of photographic materials, ensuring that resulting photomicrographs are of high quality and reproducibility.

Key Topics

ASTM E883-11(2024) addresses the following essential topics for users involved in metallography, materials science, and microscopy photography:

• Magnification: Guidelines for selecting and calibrating preferred magnification levels, ensuring photomicrographs accurately reflect specimen features.
• Reproduction of Photomicrographs: Recommendations for preparing prints and transparencies, including annotation and information that should accompany images.
• Optical Systems: Details on choosing objectives, eyepieces, and the importance of optical alignment within reflected-light microscopes.
• Illumination: In-depth discussion of light sources (e.g., Köhler, arc lamps, tungsten-halogen) and their configuration to optimize image clarity and contrast.
• Filters and Exposure: Guidance on using optical filters for both black-and-white and color photomicrography, matching film types and processing to lighting conditions, and adjusting exposure for accurate representation.
• Photographic Materials and Processing: Selection of appropriate films and photographic papers, instant-processing materials, and relevant darkroom and digital handling steps.
• Specialized Techniques: Descriptions of illumination methods such as dark field, polarized light, differential interference contrast (DIC), and sensitive tint techniques to enhance visualization of structure and phase differences.

Applications

ASTM E883-11(2024) provides practical value for professionals and laboratories engaged in metallography, materials analysis, and failure investigations, including:

• Metallurgical Quality Control: Ensuring consistent documentation and analysis of metal grain structures, inclusions, and surface treatments.
• Materials Research: Supporting characterization of new alloys, composites, and surface coatings using standard photography techniques.
• Industrial Inspection: Providing reproducible, high-quality photographic evidence for engineering assessments, product verification, and compliance with technical specifications.
• Educational and Reference Archives: Facilitating the creation of clear, annotated photomicrographs for use in teaching, publications, and historical records.
• Forensic Analysis: Enabling accurate capture of microstructural details in legal or failure analysis contexts where photographic integrity is essential.

Related Standards

Professionals using ASTM E883-11(2024) may also reference these related standards for enhanced guidance:

• ASTM E7 – Terminology Relating to Metallography
• ASTM E768 – Guide for Preparing and Evaluating Specimens for Automatic Inclusion Assessment of Steel
• ASTM E1951 – Guide for Calibrating Reticles and Light Microscope Magnifications

These standards, together with E883-11(2024), form a comprehensive foundation for photomicrography using reflected-light microscopy in metallographic and materials science laboratories. For full implementation and the latest technical updates, consult the ASTM website and manufacturer documentation for recommended microscopy equipment and materials.

Keywords: reflected-light photomicrography, ASTM E883, metallographic photography, illumination techniques, microscopy, photographic processing, materials science imaging, standard guide.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E883 − 11 (Reapproved 2024)
Standard Guide for
Reflected–Light Photomicrography
This standard is issued under the fixed designation E883; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope mine the applicability of regulatory limitations prior to use.
Specific precautionary statements are given in X1.7.
1.1 This guide outlines various methods which may be
1.5 This international standard was developed in accor-
followed in the photography of metals and materials with the
dance with internationally recognized principles on standard-
reflected-light microscope. Methods are included for prepara-
ization established in the Decision on Principles for the
tion of prints and transparencies in black-and-white and in
Development of International Standards, Guides and Recom-
color, using both direct rapid and wet processes.
mendations issued by the World Trade Organization Technical
1.2 Guidelines are suggested to yield photomicrographs of Barriers to Trade (TBT) Committee.
typical subjects and, to the extent possible, of atypical subjects
2. Referenced Documents
as well. Information is included concerning techniques for the
enhanced display of specific material features. Descriptive
2.1 ASTM Standards:
material is provided where necessary to clarify procedures.
E7 Terminology Relating to Metallography
References are cited where detailed descriptions may be
E175 Terminology of Microscopy (Withdrawn 2019)
helpful. E768 Guide for Preparing and Evaluating Specimens for
Automatic Inclusion Assessment of Steel
1.3 The sections appear in the following order:
E1951 Guide for Calibrating Reticles and Light Microscope
Referenced documents 2
Magnifications
Terminology 3
2.2 Other Standard:
Significance and use 4
Magnification 5
MSDS Mercury-Material Safety Data Sheet
Reproduction of photomicrographs 6
Optical systems 7
3. Terminology
Illumination sources 8
Illumination of specimens 9
3.1 Definitions—For definitions of terms used in this guide,
Focusing 10
see Terminologies E7 and E175.
Filters for photomicrography 11
Illumination techniques 12
4. Significance and Use
Instant-processing films 13
Photographic materials 14
4.1 This guide is useful for the photomicrography and
Photographic exposure 15
Photographic processing 16 photomacrography of metals and other materials.
Keywords 17
4.2 The subsequent processing of the photographic materi-
Suggestions for visual use of metallographic Appendix
microscopes X1
als is also treated.
Guide for metallographic photomacrography Appendix
X2
5. Magnification
Electronic photography Appendix
X3
5.1 Photomicrographs shall be made at preferred
magnifications, except in those special cases where details of
1.4 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the the microstructure are best revealed by unique magnifications.
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
1 3
This guide is under the jurisdiction of ASTM Committee E04 on Metallogra- The last approved version of this historical standard is referenced on
phyand is the direct responsibility of Subcommittee E04.03 on Light Microscopy. www.astm.org.
Current edition approved April 1, 2024. Published April 2024. Originally Available from United States Environmental Protection Agency (EPA), William
approved in 1982. Last previous edition approved in 2017 as E883 – 11(2017). DOI: Jefferson Clinton Bldg., 1200 Pennsylvania Ave., NW, Washington, DC 20460,
10.1520/E0883-11R24. http://www.epa.gov.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E883 − 11 (2024)
5.2 The preferred magnifications for photomicrographs, are: 7.5 The resolution of the microscope depends primarily on
25×, 50×, 75×, 100×, 200×, 250×, 400×, 500×, 750×, 800×, the numerical aperture of the objective in use (1) . The term
and 1000×. empty magnification is used to describe high magnifications
(above approximately 1100 times the numerical aperture of an
5.3 Magnifications are normally calibrated using a stage
objective), which have been shown to offer no increase in
micrometer. Calibration procedures in Guide E1951 should be
image resolution. Nevertheless, some types of information,
followed.
such as the distance between two constituents, may be more
easily obtained from microstructures examined at moderate
6. Reproduction of Photomicrographs
empty magnifications.
6.1 Photomicrographs should be at one of the preferred
8. Illumination Sources
magnifications. A milli- or micrometre marker shall be super-
imposed on the photomicrograph to indicate magnification, in
8.1 Metallographic photomicrography typically uses Köhler
a contrasting tone. The published magnification, if known,
illumination. To obtain Köhler illumination, an image of the
should be stated in the caption.
field diaphragm is focused in the specimen plane, and an image
of the lamp filament or arc is focused in the plane of the
6.2 Photomicrograph captions should include basic back-
aperture diaphragm. Specific steps to obtain Köhler illumina-
ground information (for example, material identification,
tion vary with the microscope used. The manufacturer’s
etchant, mechanical or thermal treatment details) and should
instructions should be followed closely.
briefly describe what is illustrated so that the photomicrograph
can stand independent of the text. 8.2 For incandescent lamps, the applied voltage determines
the unit brightness and the color temperature of the source.
6.3 Arrows or other markings, in a contrasting tone, shall be
Evaporated tungsten blackens the envelope, resulting in dimin-
used to designate specific features in a photomicrograph. Any
ished brightness and color temperature as the lamp ages.
marking used shall be referenced in the caption.
Tungsten-halogen lamps minimize envelope blackening, main-
taining constant brightness and color temperature for most of
7. Optical Systems
their life. The high brightness and 3200 K color temperature of
7.1 Microscope objectives are available in increasing order
these lamps makes them especially suitable for color photomi-
of correction as achromats, semiapochromats (fluorites) and
crography.
apochromats (see Terminologies E7 and E175). Plan objectives
8.3 With arc sources, brightness per unit area is substan-
are recommended for photographic purposes because their
tially higher than that from any incandescent source. Their
correction provides a flatter image. The objective lens forms an
spectral output contains high energy spikes superimposed on a
image of the specimen in a specific plane behind the objective
white-light continuum. They also contain significant ultraviolet
called the back focal plane. (This is one of several possible real
(UV) and infrared (IR) emissions that should be removed for
image planes, called intermediary planes, where reticles may
eye safety (and for photographic consistency, with UV); see
be inserted as optical overlays on the image.)
8.4, 11.3.1, and 11.5.2.
7.2 The eyepiece magnifies the back focal plane (or other) 8.3.1 Xenon arcs produce a spectral quality close to daylight
intermediary image for observation or photomicrography. Eye- (5600K), with a strong spike at 462 nm. Strong emissions in
pieces are sometimes also used to accomplish the full correc- the IR should be removed. Xenon arcs that do not produce
tion of the objective’s spherical aberration and to improve the ozone are recommended.
flatness of field. 8.3.2 Carbon arcs have a continuous output in the visible
portion of the spectrum, with a color temperature near 3800K
7.2.1 The pupil of the observer’s eye must be brought to
and a strong emission line at 386 nm.
coincidence with the eyepoint of the visual eyepiece to view
8.3.3 Mercury arcs have strong UV and near-UV output,
the entire microscopical image. High-eyepoint eyepieces are
and are particularly useful to obtain maximum resolution with
necessary for eyeglass users to see the entire image field.
a blue filter. The color quality is deficient in red; it cannot be
7.2.2 Most microscopes have built-in photographic capa-
balanced for color photomicrography. Warning—Mercury has
bilities that use an alternate image path through the microscope
been designated by EPA and many state agencies as a hazard-
leading to a camera attachment port or to a viewscreen. A
ous material that can cause central nervous system, kidney, and
projection eyepiece delivers the image to the camera port or
liver damage. Mercury, or its vapor, may be hazardous to
screen.
health and corrosive to materials. Caution should be taken
7.3 Intermediate lenses (relay or tube lenses) are often
when handling mercury and mercury-containing products. See
required to transfer the specimen image from the intermediary
the applicable product Material Safety Data Sheet (MSDS) for
plane of the objective to that of the eyepiece. They may also
details and EPA’s website (http://www.epa.gov/mercury/
add their own magnification factor, either fixed or as a zoom
faq.htm) for additional information. Users should be aware that
system.
selling mercury or mercury-containing products, or both, in
your state may be prohibited by state law.
7.4 The objective, the eyepiece, and the compound micro-
scope (including any intermediate lenses) are designed as a
single optical unit. It is recommended to use only objectives
The boldface numbers in parentheses refer to the list of references at the end of
and eyepieces which are intended for the microscope in use. this standard.
E883 − 11 (2024)
8.3.4 Zirconium arcs have strong spectral output lines in the diameter. This can be observed by removing the eyepiece and
near IR, requiring filtration. Within the visible region, they are inspecting the back of the objective, either directly or with a
rated at 3200K color temperature. pinhole eyepiece. The aperture diaphragm should never be
used as a light intensity control.
8.4 Arc lamps require heat protection for filters and other
optical components, and certainly for eye safety. Infrared 9.5 See Fig. 1 for an illustration of a typical vertical
removal may be obtained by: “hot” mirrors in the illumination illumination system.
beam to reflect IR while transmitting visible light; heat-
absorbing filters to transmit visible light while absorbing IR, 10. Focusing
for example, solid glass filters or liquid-filled cells.
10.1 Sharp focus is necessary to obtain good photomicro-
8.5 A detailed discussion of illumination sources and the graphs.
quality of illuminants is given by Loveland (2).
10.2 There are two systems for obtaining sharp focus:
8.6 Some advice on using metallographic microscopes for ground-glass focusing and aerial image focusing.
visual observation has been compiled in Appendix X1.
10.2.1 For ground-glass focusing, relatively glare-free sur-
roundings and a magnifier up to about 3× are required. To
9. Illumination of Specimens
focus, the focusing knob is oscillated between underfocus and
9.1 Photomicrographs are made with a compound micro- overfocus in succeedingly smaller increments until the image is
scope comprised at least of an objective lens and an eyepiece sharp.
with a vertical illuminator between them. Field and aperture 10.2.2 There are four possible variations for focusing an
diaphragms, with a lamp and lamp condenser lenses, are aerial image.
integral parts of the system. The microscope should allow 10.2.2.1 The simplest case is a transparent spot on a
sufficient adjustment to illuminate the field of view evenly and ground-glass containing a fiduciary mark in the film plane. The
to completely fill the back aperture of the objective lens with specimen image is focused to coincide with the fiduciary mark,
light. using a magnifying loupe of about 3× to 5×. When the focus is
correct, the specimen image and the fiduciary mark will not
9.2 The vertical illuminator is a thin-film-coated plane glass
move with respect to each other when the operator’s head is
reflector set at 45° to the optical axis behind the objective. It
moved.
reflects the illumination beam into the objective and transmits
10.2.2.2 A second case uses a reticle fixed within the optical
the image beam from the objective to the eyepiece. In some
system at an intermediary plane. Focusing is a two-step
microscopes prism systems are used to perform this function.
process: focus the eyepiece on the reticle; bring the image into
9.3 The field diaphragm is an adjustable aperture which
focus against the reticle figure.
restricts the illuminated area of the specimen to that which is to
10.2.2.3 In the third case, a reticle is inserted into a focusing
be photographed. It eliminates contrast-reducing stray light.
eyepiece. Depending on equipment used, this can be either a
The field diaphragm is also a useful target when focusing a
two or three-step process: focus the reticle within the eyepiece;
low-contrast specimen.
next, set the proper interpupiliary distance, if required (some
9.4 The aperture diaphragm establishes the optimum bal- equipment requires a specific interpupiliary distance for eye-
ance between contrast, resolution, and depth of field. It should piece focus to coincide with camera focus); then focus the
be set to illuminate about 70 % of the objective’s aperture image coincident with the reticle.
FIG. 1 Vertical Illuminating System for a Metallurgical Microscope
E883 − 11 (2024)
10.2.2.4 The fourth case uses a single-lens reflex camera filter is used with a color complementary to that of the feature
body, where the camera focusing screen is the plane of (for example, a cyan filter for reddish copper plating; a blue for
reference. An eyepiece magnifier for the camera is an impor- yellow carbonitride particles). When maximum detail in a
tant accessory for this case. An aerial image focusing screen is colored phase must be shown, choose a filter with the same
preferred. color as the phase.
10.3 The critical focus point is affected by both the principal 11.5 Filters for Color Photomicrography:
illumination wavelength in use and the size of the aperture 11.5.1 Color photomicrography generally requires filtration
diaphragm. Final focusing should be checked with all filters, to balance the light at the image plane to the color temperature
apertures, and other components set for the photomicrograph. specified by the film’s manufacturer. Most transparency and
negative color films are balanced for use with daylight at 5600
K. Some films are balanced for tungsten source lighting at
11. Filters for Photomicrography
either 3200 K or 3400 K.
11.1 Photomicrographs require filtration of the light source.
11.5.2 Color films record ultraviolet light as blue. Since
This section describes filter types and their uses.
different metals reflect varying amounts of ultraviolet light, the
11.2 Each filter selectively removes some wavelengths from
simplest solution is to remove all ultraviolet light, as in 11.3.1,
the transmitted beam of light. Two types of filters, interference
and rebalance by adding compensatory blue filters.
and absorption, can be used for this purpose.
11.5.3 Table 1 lists filter recommendations appropriate for
11.2.1 Interference filters act as selective mirrors. By means
color photomicrography. These include strong conversion fil-
of coatings on a glass substrate, they selectively transmit
ters (the blue 80 series and the orange-yellow 85 series) and
certain wavelengths while reflecting all others. These filters
weaker light-balancing filters (the yellow 81 series and the
may be used in high-energy light beams. The mirrored side of
blue 82 series). Because of individual variations in equipment
the filter should face the light source. (The hot mirrors in 8.4
and other filtration (for example, IR and UV removal), some
are interference filters.)
fine tuning is usually required with color correction filters.
11.2.2 Absorption filters are dyed substrates of glass,
These filters are commonly used in color printing, and are
plastic, or gelatine. They absorb some wavelengths of light and
available in sets containing various strengths of red, yellow,
transmit the balance. Through their absorption, they can
green, cyan, blue, and magenta.
become overheated and damaged if placed in high-energy light
11.5.4 The correct color balance for any color film can be
beams without protection. The usual protection is either an
determined using a first-surface mirror as the specimen (see
interference filter or a liquid-filled cell placed in the beam
Note 1). After the recommended filtration from Table 1 has
before the absorption filter. Wratten gelatine filters are used
been inserted, a series of test exposures of the mirror is made
below as examples (3). Many similar glass and plastic filters
with several color correction filters, until a neutral gray result
are also available.
is obtained. (Because of differences in manufacturing, different
films with the same color temperature ratings may require
11.3 Certain general purpose filters have application in both
slightly different groups of filters to achieve the correct color
color and black-and-white photomicrography.
balance.)
11.3.1 Ultraviolet light can be removed with an interference
filter, a glass or gel filter from the Wratten #2 series, or a liquid
NOTE 1—It is important to have a standard to balance the effective
cell filled with a sodium nitrite solution (2 % NaNO is used
illumination of the system to photographic neutrality. Aluminum is
for a 1-cm path. It should be proportionately stronger or photographically neutral throughout the visible and UV wavelengths. A
first-surface aluminum mirror can be used as a repeatable standard. (A
weaker for other cell path lengths). Ultraviolet light must be
protective chromium overcoating destroys the neutrality, but a thin silicon
removed from arc lamps for eye safety, and should be removed
monoxide protective layer is acceptable.)
for color photomicrography, as explained in 11.5.2.
11.3.2 Gray neutral density filters reduce the intensity of a
12. Illumination Techniques
light beam equally across the visible spectrum. They are made
12.1 Metallographic specimens should be illuminated to
in interference and absorption types in many different
reveal significant structural details with optimum contrast and
densities, for example, the Wratten #96 series. They are useful
resolution, and with sufficient brightness for accurate photo-
for eyepiece work with an arc source, and to modify the
graphic recording.
brightness of any tungsten source without changing its color
12.2 With bright field illumination, polished areas of the
temperature.
specimen that are perpendicular to the light path reflect
11.4 Filters for Black and White Photomicrography:
11.4.1 Generally, a monochromatic filter is used to optimize
TABLE 1 Suggested Filtration for Color Photomicrography
the resolution of the objective. With achromats, a green
Film Color Balance Daylight 3200 K 3400 K
centered around 550 nm is used; for apochromats and
Light Source Wratten Filter Number
semiapochromats, a blue centered around 486 nm provides
Tungsten 80A + 82A 82A 82C
slightly better resolution, but with a penalty of more difficult
Tungsten-halogen 80A None 82A
visual focusing. Zirconium arc 80A None 82A
Carbon arc, 4.5 amp 80C 81C 81A
11.4.2 Cases arise where the visual contrast can be im-
Carbon arc, 10 amp 82C + 82C 81EF 81C
proved to emphasize a colored feature in the microstructure.
Xenon arc None 85B 85
The color will reproduce darker in the photomicrograph if a
E883 − 11 (2024)
incident vertical illumination back into the objective lens and 12.7 Differential Interference Contrast—(DIC or Nomarski
appear bright (see 9.2 and Fig. 1). Features such as inclusions illumination) This illumination technique shows edges of
and etched grain boundaries have edges that are inclined to the discontinuities on specimens as variations in brightness. Color
polished surface and reflect light away from the objective lens, contrast can be added as an additional indication of level
making them appear dark. variation. The method is termed differential because very
minor discontinuities are emphasized, whereas slightly angled
12.3 Oblique illumination is similar to bright field, but is
slopes are displayed almost as if they were perfectly normal to
nonspecular, with the light impinging on the specimen at an
the optical axis; for example, a cylindrical phase looks flat with
oblique angle to the optical axis. It is obtained by decentering
fairly sharp edges. A modified Wollaston prism located at the
the aperture diaphragm, or by tilting the specimen slightly (4).
rear focal plane of the objective splits the illumination beam
The technique is useful to enhance specimen surface relief and
into two parallel beams, separated in phase by one-quarter
to determine if specific features are pits or projections, since
wavelength. Any alteration of the optical path by the specimen,
shadows are cast by nonplanar features. Resolution decreases
by either path length (feature height) or refractive index,
as the illumination is made more oblique. (It is important that
produces an interference pattern in the image beams. As the
the decentered diaphragm be completely imaged in the rear
beams return through the DIC prism, they are reunited and the
focal plane of the objective to keep the illumination reasonably
interference effect appears as a variation in brightness and
uniform across the field.)
color. Most microscopes allow translation of the DIC prism to
12.4 Dark field illumination is obtained by directing light to
produce different color displays as well. DIC has several
the specimen along the outside of the objective, blocking out
unique advantages: Since the full back aperture is illuminated,
the illumination passing through the lens. These outside rays
the full resolution of the objective is utilized; the interference
are diverted onto the specimen plane obliquely by a conical
plane is very shallow, keeping out-of-plane detail from inter-
reflector. No specular reflections enter the objective. Only
fering; there is an oblique appearance as an additional clue to
features that are tilted with respect to the surface (for example,
level differences. Useful applications of DIC are: judging
grain boundaries, pits, and inclusions) will reflect light into the
adequacy of specimen preparation for automated microscopy,
objective. These features will appear bright against a dark
as in Practice E768; display of surface relief, including changes
background. Image contrast is higher in dark field illumination
of a few nanometres at abrupt edges.
than in other modes and will frequently reveal specimen detail
that would be completely obscured with other kinds of illumi-
13. Instant-Processing Films
nation.
13.1 These materials yield photographic images within
12.5 Polarized light reveals grain structure and twinning in
seconds after exposure (5). Both color and black-and-white
metals with a hexagonal lattice structure, such as beryllium, versions are available. All use variations of the diffusion-
tin, titanium and zinc. Polarized illumination is produced by
transfer process, with each frame developed individually after
optical components consisting of calcite prisms or Polaroid™ exposure.
filters. They selectively provide an image consisting of polar-
13.1.1 Instant materials should be exposed so that the
ized light reflected from a specimen surface and scattered lightest (white) tone in the image is reproduced as the brightest
depolarized light from nonplanar surface features. Polarized
tone in the picture. (Shorter exposures will produce muddy
light reacts differently when reflected from isotropic and whites, while longer ones will give insufficient separation
anisotropic material lattices. For a cubic material, the micro-
between the lighter tones.)
scope field appears dark because most of the light reflected 13.1.2 The majority of the instant materials are of peel-apart
from the specimen is absorbed by the system. With an
construction, where the positive print is detached from the
anisotropic material, the plane polarized beam reflected from processing packet after development and the rest of the unit is
the specimen surface either becomes elliptically polarized or
discarded. A useful variation of this provides a transparent
the polarization plane is rotated. In both cases, the system now negative as well, for multiple print production by wet-process
passes a portion of the reflected light through to the viewing
darkroom methods. Excellent photographic prints can be made
system. Polarized light is also used with optically inactive from the negative instant films with great degrees of enlarge-
cubic metals that are treated to produce an anisotropic surface
ment possible. (In order to optimize the exposure of the
film on the substrate. It is also useful to identify optically active negative with a positive/negative film, the positive will be
inclusions and phases and in defining domains in ferromagnetic
overexposed, and therefore not considered an acceptable print.)
materials.
13.1.3 The monopack materials, both black-and-white and
color, require adapters that are unlike those normally fitted to
12.6 Sensitive Tint—Many metals and nonmetallic crystals
metallographic equipment. No processing control is possible.
are birefringent. Plane polarized light is reflected from them as
With some exceptions, monopack prints should not be cut. The
elliptically polarized light, which has a component not extin-
use of the more adaptable peel-apart materials may be the
guished by the system. If a quartz or gypsum sensitive tint filter
better choice for metallography.
(also known as a λ compensator, a full-wave plate or a
first-order compensator) is used, a magenta color is seen with 13.2 Processing Instant Films—All instant materials, both
cubic metals and all birefringent metals appear in vivid color peel-apart and monopack, are processed by pulling the picture
contrasts. Nodular cast iron demonstrates this effect particu- unit through an accurately-spaced roller pair. A chemical pod at
larly well, if a rotatable stage is used. the leading edge is ruptured and the contents spread throughout
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the unit by the rolls, starting the development action. The brightness ratio of 1:3, dark field and polarized light images
reaction goes to completion according to the time-temperature can exceed a 1:100 ratio. Reflection prints can at best repro-
relationship supplied with the film.
duce a 1:30 brightness range. A film chosen for the first
13.2.1 The picture unit must be pulled in a straight line example should be capable of expanding the brightness range
through the rollers, at a constant speed, to secure uniform
(contrast) by exposure and development control. A film for the
1 1
processing. A pull-time of ⁄4 to ⁄2 second is suggested for
latter example should compress the contrast of the original
peel-apart materials. Monopack instant materials permit no
image. Typically, a film classified as high-contrast would be
control over processing time, since the self-developing reaction
used in the first case, while a medium-to-low contrast material
is controlled by the film holder and proceeds to completion
would be chosen for the other. (The extremely high-contrast
without attention from the user.
lithographic films used for graphic arts purposes are excluded
13.2.2 The roller pair should be kept clean, since even fine
here. Their useful range of tonal reproduction is too restricted.)
debris on the rolls will cause uneven reagent spreading and
14.5.1 The contrast potential of any film material is most
picture nonuniformity.
easily expressed graphically as the film’s characteristic curve
13.2.3 Black-and-white peel-apart materials are best pro-
published for all films in the manufacturers’ literature. As an
cessed for at least the recommended time for the type involved.
example of a film’s potential, such a curve is schematically
Extended processing up to three minutes is permissible. Be-
represented in Fig. 2. As the exposure increases on the
yond this, problems may be encountered as the units are
horizontal axis, the corresponding photographic effect (black-
peeled.
ening of the film) increases on the vertical axis. This effect
13.2.4 Improved contrast and color saturation can be
becomes more prominent with increasing time of development,
achieved with color peel-apart materials by processing to a
as indicated by the individual numbers on the curves. The
two-minute standard, rather than the recommended one minute.
useful part of a film’s sensitivity range is the mid-portion,
The color balance will shift toward cyan, which can be
where the slope is relatively constant, indicating a proportional
corrected by adding some red to the filter pack.
change in density with a proportional change in exposure
(shown on Fig. 2 by range m-n). The slope of the curve rises
14. Photographic Materials
more steeply as development proceeds and thus the contrast of
14.1 Wet-Process Materials: General and Black-and-
the film image increases with increasing development.
White—Conventional photographic materials provide an al-
14.6 Several properties of negative emulsions that must be
most unlimited choice of conditions for recording an image.
considered are: overall light sensitivity (film speed), spectral
Many of the readily available products can be usefully em-
sensitivity, resolving power, graininess, and contrast potential.
ployed in metallography. References (4-7) are recommended
All of these qualities cannot be optimized at once in any film,
reading to learn the complete photographic characteristics of
hence choices must be made to suit the needs of the photomi-
the products, as well as the terminology used to describe them.
crograph.
14.2 The essential construction of a photographic material
14.6.1 Films are rated for general pictorial purposes by film
consists of a carrier base with a light-sensitive layer of silver
speed numbers, for example, ISO speeds or DIN indices, with
halides in gelatine, commonly called the emulsion. Negative
the higher rankings having increased light sensitivity. These
and projectable emulsions are on transparent flexible acetate or
rankings are not usually significant in metallography, since it is
polyester film bases, while reflection print materials have white
seldom important to make a rapid exposure. A faster film will
paper or paper/plastic composite bases.
probably be more convenient with a dim image, but if
14.3 The most common materials are negative-acting, that
exposures over several seconds are required, the degree of
is, exposure to light and subsequent chemical processing
departure from reciprocity will usually be the controlling
displays an image on a film wherein the tonal values of the
consideration in film choice (see 15.6).
original scene (microscopical field) are reversed. This is
14.6.2 Some films record in the green and blue wavelengths
subsequently printed by light exposure through the negative
much more efficiently than their overall film speeds would
onto photographic paper, where a positive image (the negative
indicate and are thus good choices for black-and-white photo-
of the negative film image) is reproduced with similar chemical
micrography. Orthochromatic films are especially useful; their
steps.
red-blindness is inconsequential with green or blue filtration
14.4 Some materials, either by controlled pre-exposure
while permitting use of a red safelight in the darkroom.
during manufacture or by specialized processing, yield a
14.6.3 The resolving power of an emulsion defines the
positive image directly and are called positive-acting. The
closest spacing of points in an image that can be reproduced by
principal uses are for projectables (slides) and negative dupli-
the film as individual points. In general, any film which can
cation.
resolve 20 or more lines per mm (10 line pairs per mm) with
a low contrast image will be adequate for making same size
14.5 Negative film materials are of the most concern for
metallography. The film chosen to record a microscopical (contact) prints. Films with higher resolutions are required for
enlarged prints, with the enlarging factor controlling the film
image must be able to reproduce the tonal values in the image
in their correct relationship to produce satisfactory prints. The resolution needed (for example, a 4× enlargement would
require an emulsion capable of resolving 4 × 20, or 80
film choice is in part dictated by the subject matter to be
recorded-a simple steel image in bright-field may have only a lines/mm).
E883 − 11 (2024)
FIG. 2 Optical Density Versus Logarithm of Exposure for Photographic Materials
14.6.4 Graininess of a photographic emulsion is usually a those intended for contact printing (relatively low sensitivity)
function of the emulsion speed (ISO index), with faster films and those for projection printing (higher sensitivity). A variety
tending to be grainier. The presence of grain is more an of contrast grades are available in both types, to balance the
annoyance factor than a technical defect. However, when image contrast on the film (8). Some enlarging papers are
enlargements are required, the choice of finer-grained emul- offered in multiple-contrast versions, where the paper contrast
sions will produce superior prints.
can be changed with appropriate magenta and yellow filtration.
14.6.5 A film with a suitable contrast index should be
14.9 Printing materials have emulsions coated on either
chosen to balance the contrast class of the specimen photo-
paper or plastic-coated (commonly called RC) bases. While the
graphed. Therefore, flat, low-contrast images require a high
traditional fiber paper base is likely to have the longest useful
contrast index material, in the order of 1.4 to 1.6, to produce a
life and reproduce a slightly higher brightness range, the
satisfactory print. Most metallographic images have more
plastic-coated types are much more convenient to handle,
inherent contrast and can be adequately recorded with a
especially in a nonautomated darkroom.
contrast index of 1.0. Extremely contrasty images (some dark
field or polarized light images) are best recorded with materials
14.10 Wet-Process Materials: Color Considerations—All of
of contrast index near 0.7 (which is in the useful range for
the considerations discussed in 14.1 – 14.6 also apply to color
general photography).
materials, but there are others as well. All color films are really
tri-pack films, each with one emulsion layer responding to
14.7 Negative materials must be printed to provide a usable
ultraviolet/blue, green, and red radiation, respectively. Because
image. Any reflection print using a glossy stock is restricted to
of this complexity, little variation in exposure or development
reproducing a brightness range to a maximum of 1:30. Smooth
is possible and the manufacturer’s instructions must be fol-
nonglossy, matte, and textured paper stocks will produce
lowed closely. Especially important are the color temperature
decreasing brightness ranges, in the order listed. For maximum
of the light (see 11.5.1) and the exposure time required.
definition of metallographic images, glossy stock is always
suggested.
14.11 Color positive (slide) films are convenient to use. The
14.8 Like films, printing papers have different speed emul- emulsion exposed in the microscope is reversal processed to
sions available. The only important distinction is between yield a transparency directly. Emulsions are available which
E883 − 11 (2024)
are balanced for daylight quality, 3400 K light and 3200 K and numerical aperture of the objective, as well as the exposure
light. All brands except Kodachrome™ can be user-processed. time, must all be recorded as the calibration conditions with
Direct-reversal print-making processes are available, or an that film processed in that way. Obviously, changes in any of
internegative film can be prepared from the slide for subse- the conditions will require another calibration. This can often
quent color printing.
be avoided by making an instant-film test with the new
conditions, and using the relationship:
14.12 Color negative film must be printed (to either a
reflection print or a transparency) for viewing. Except for a few new time 5 old calibrated time (1)
~ !
sheet and large roll films balanced for 3200 K, all are designed
× new instant print time / old instant print time
~ ! ~ !
for daylight-quality illumination and all may be user-
processed. Since printing is required, a gray scale (see 15.11)
15.2.1.2 A simple brightness meter, either built into the
should be exposed as a guide for the printer. Alternatively, an
microscope or used as an external accessory, makes exposure
instant color print can be used for a sample.
determination simpler. External probes are used either in the
eyepiece tube or at the ground-glass screen of a sheet film
15. Photographic Exposure
camera back. Built-in meters sample the image beam light in a
15.1 Exposing Wet-Process Materials: General and Black-
fixed location within the microscope. With the film type and
and-White—After a film is chosen according to the criteria of
film processing necessarily held constant, the only factors that
14.6.5, a suitable exposure must be made to record all of the
need to be known are the correct exposure time for a certain
tonal values present in the image on the straight-line portion of
brightness value with a specified filtration. (Photocells often
the characteristic curve, as shown by m-n in Fig. 2. The
have color sensitivities that differ across the spectrum from
immediate problem is to determine the proper exposure, which
film color sensitivities. Thus, any filtration change will require
is approached differently for negative and reversal (positive)
a new calibration.) As the brightness value changes, a propor-
materials, including instant-processing films.
tional change in the exposure time will be required. A simple
15.2 The simplest case in photomicrography involves rever-
two-point calibration graph will usually suffice for external
sal materials, including instant-processing films. The exposure probes, while microscope manufacturers provide calculation
must be sufficiently long so that the lightest (white) tone in the
guides for built-in brightness devices. In cases where the
image is reproduced as the brightest tone in the picture.
microscope eyepiece magnification need not be the same as the
(Shorter exposures will produce muddy whites, while much
film plane magnification (usually applies to microscopes with
longer ones will give insufficient separation between the light
a bellows camera station), the indicated exposure time must be
tones.) The correct exposure time, which is a function of the
modified if the film plane magnification is changed, unless a
brightness at the film plane, must be experimentally deter-
film-plane brightness probe is used. The calculation is:
mined to calibrate the system, as explained below. Factors
new magnification
influencing film-plane brightness are: type of lamp and voltage new time 5 old ~calibrated! time × (2)
S D
old magnification
or power setting, filtration, aperture diaphragm opening, mag-
nification at the film plane, and the numerical aperture of the
15.2.1.3 The next step in sophistication is a photometer with
objective. Once calibrated, the same conditions will reproduce
built-in provision for entering film speeds, typically marked as
the same film exposure without further testing.
ISO indices. In this case, the meter calculating dial is adjusted
15.2.1 A calibration exposure series holds all of the film-
after calibration to show the effective exposure index for the
plane brightness factors from 15.2 constant, while varying the
film that gives the experimentally determined exposure time at
exposure time around an estimated time. (The estimated time
the brightness value used in the calibration. Thereafter, with the
can be quickly approximated from a trial exposure with an
same film, processing and filtration, the effective exposure
instant-print material of approximately the same white-light
index is simply dialed in, the reading made, and the calculator
1 1
film speed.) A suggested sequence of test exposures is ⁄8, ⁄4,
dial shows the correct exposure time directly. (In the case of a
⁄2, 1, 2, 4, and 8 times the estimated exposure. With roll film,
modified conventional exposure meter at the eyepiece with a
one frame per exposure level is exposed. With sheet film the
bellows-type camera back, the extra calculation in Eq 2 is still
entire series can be put on one sheet, using a premarked dark
necessary for film magnifications other than the calibrated
slide to mask successive portions of the frame. (In this case,
one.)
because the exposures will be additive, the series should be ⁄8
15.2.1.4 Some microscopes will automatically make the
1 1 1
+ ⁄8 + ⁄4 + ⁄2 + 1 + 2 + 4 times the estimated exposure, with
correct exposure directly upon releasing the exposure button,
the dark slide advanced into the image area after each
based upon an automatic integration of brightness and pro-
exposure, according to the markings.) The dried film is directly
grammed film exposure index. A one-point calibration is all
compared to the microscopical image to judge the most
that is required to find the proper exposure index for each
successful exposure. This time value is used in one of the
film/processing/filtration condition.
following ways, depending on the sort of light-measuring
equipment available at the microscope. 15.3 Negative materials must have sufficient exposure to
record the darkest (but nonblack) part of the image on the film,
15.2.1.1 With no exposure measuring device, the calibration
becomes strictly empirical. The microscope, filtration, lamp so that it can be printed in its proper relationship to all of the
other tones in the image. All of the other (brighter) tones in the
(including voltage for filament lamp or power setting for arc
lamp), aperture diaphragm setting, film plane magnification image will therefore record as darker images on the negative.
E883 − 11 (2024)
Calibration for this follows the scheme of 15.2.1, but photo- 15.9 Exposing Wet-Process Materials: Color
graphic printing of the test negatives is required to judge the Considerations—As mentioned in 11.5.1, color emulsions are
optimum exposure to use for the film calibration.
balanced in manufacture to properly respond to light of a
specified color quality, either daylight (at 5600 K) or tungsten
15.4 All of Section 15 has thus far applied to relatively
source (3200 or 3400 K). Inevitably, filtration is required to
bright microscopical images-bright field, differential interfer-
produce the correct color temperature in metallography. Other
ence contrast or sensitive tint. With polarized light and dark
components in a microscope system (such as heat absorbers,
field, the images are typically very dark overall, with important
lenses, prisms, and mirrors) will alter the illumination quality
brighter spots. New calibrations are required for these, and they
of the beam, even if the lamp has the same color balance as the
will usually remain empirical, since very few exposure-
film emulsion.
measuring devices have sufficient sensitivity to respond to the
dim images produced. Furthermore, the correct exposure is that
15.9.1 The blue-sensing layer of a color emulsion depends
which properly records the bright areas (which may be only
on a consistent amount of ultraviolet to respond correctly.
points) without regard to the relative brightness of the darker
Metals vary widely in their UV reflectance, making this a
background.
constant so
...