Kerf Patterning on Animal Cremains: Preliminary Analysis

of Microscopy Methods

Christopher E. Barrett1, Nambi Gamet1

1Anthropology Department, Western Washington University, 516 High St., Bellingham, WA 98225

Abstract

Introduction

Materials & MethodsResults

Discussion

In Forensic science reconstruction methodologies are critical to the

assessment and authentication of human behavior after time of action.

Archeological samples can present evidence of burning and thus provide

time depth to the issues involved (Ubelaker, 2009). Fire has been a

common method for the destruction of evidence in homicides, accidental

deaths, bombings, and aircraft accidence (Porta et al., 2013; Ubelaker,

2009; Alunni et al., 2014). Fire can be employed to destroy forensic

evidence in order to mislead or remove identification and reconstruction

of behavior. Contemporary research and case studies have greatly

augmented knowledge regarding the effects of extreme heat on

incinerated remains or cremains. Resulting from these scholarly efforts,

enhanced interpretation is now possible on such issues as:

• the extent of recovery

• reconstruction

• trauma

• individual identification

• color variation

• DNA recovery

Sharp force trauma and cut mark analyses to date have been intermittent

and superficially researched across a range of disciplines, despite its

potential to significantly contribute to anthropological investigation

(Herrman and Bennett, 1999; Tennick, 2012;). The use of fire is an

attempts to obscure a body is commonly encountered, however, fire does

not necessarily destroy evidence of trauma on bone (Robbins et al.,

2015). Advanced microscopy techniques such as scanning electron

microscopy (SEM) may also provided enhanced observational power

forensic reconstructions (Bartelink and Wiersema, 2001; Kooi and

Fairgrieve, 2013; Marciniak, 2009; Robbins et al. 2015).

Cremains are found within many broad anthropological contexts induced by

both human behavior as well as potentially stochastic environmental events,

adding to the challenge of reconstruction efforts (Alunni et al., 2013; Porta et

al,. 2013) . Ostensibly, enhanced observational methodologies from

developing x-ray and microscopy technologies, like SEM, have potential to

remove limitations met by other forms of observation and reconstruction

techniques, standard in forensics and anatomical methods. This study

recommends using an SEM for the examination of saw cuts in burnt bone

(Robbins, 2015).

Archaeological field methods and research using broad remote sensing

technologies demonstrate an emphasis on conservation as well as non-

invasive non-destructive processes in sample extraction, preparation, and

analysis. In culture resource management, archaeological excavation and

surveying has political and corporate applications while relying on

ecologically and sociocultural sensitive protocols. A social consciousness

underrepresented in principle ecological, sociological, and behavioral

research that is non-anthropological in origin. Enhanced observational

techniques and methodologies are made possible with progressive

equipment and technology. With additional observational information

provided by advanced microscopy, there are increasing opportunities for

multidisciplinary work.

A frequently overlooked element in the analysis of burned human remains is

reconstruction. Reconstruction provides a more holistic opportunity for

morphological interpretation and can greatly facilitate determinations of

human vs. non-human animal and recognition of specific skeletal elements.

Reconstruction can also increase the probability of identification and

recognition of trauma (Porta et al., 2013; Robbins et al., 2014; Rickman

2014; Ubelaker, 2002; Ubelaker, 2009).

Limitations and future ideas: SEM images of unburnt samples were not

taken, which would have provided further analyses for EDS spectrum

comparisons prior to and after incinerating activity. Potential follow up studies

may include EDS spectrum analyses of bones preserved in various

preservation mediums. Reconstruction capabilities could be evaluated using

metal residue analyses of metal blunt force trauma on bone.

We investigate the utility of scanning electron microscope (SEM)

methodologies in observing saw kerf patterning on burnt bone cut with

different types of saws. SEM analysis of kerf walls provide observations

that stereomicroscopes cannot. Kerf wall observations and interpretations

on cremains found within archaeological and forensic contribute to SEM

validity in methodologies of anthropological investigations.

We divided one Bos taurus, one Equidae, and two Cervus elaphus long

bones into three 9 cm segments using four different tools. Incineration of

bone segments was completed using a fire pit. Temperatures were

monitored using a Digi-Sense thermocouple thermometer. Thin sections

were prepared from the cut portions of each segment after burning.

Observations of kerf patterning were made using light and SEM.

Fractures and kerf wall patterning were observed using two different

microscopy methods. SEM provided further observations in comparison

to stereomicroscopes of kerf wall characteristics in cremains.

When comparing SEM and light microscopes the SEM provides a superior

observational method for the observation of kerf patterning in cremains. With

the SEM kerf pattern characteristics became very clear. Shallow false starts as

well as individual striations are very clear when compared to the stereo-light

microscope. The SEM also provided images of the heat induced fractures as

well as fractures due to weathering otherwise not visible using standard light

microscopy.

Two SEM/EDAX analyses were taken, providing elemental compositions of the

interior kerf floor and patterns as well as the superficial bone. Energy-

dispersive X-ray spectroscopy (EDS) analyses differed between the two site.

Kerf flooring, although observationally heterogeneous, yielded a homogenous

EDS spectrum distribution.

Figure 4. Reciprocating saw cutting by Bos taurus A. Fisheye image of burnt

kerf mark. B. Photo of unburnt kerf mark using stereo-light microscope. C.

Photo of burnt kerf mark using stereo-light microscope. D. Image of kerf mark

and location of EDAX analysis. E. Image of kerf mark and EDAX analysis. F.

EDS spectrum of kerf floor. G. EDS spectrum of superficial surface.

A.

B. C.

D. E.

F. G.

Marisa Acosta, Peter Thut, Charles Wandler, Mike Etnier, and Sarah Campbell

for constructive edits, sample collection, equipment acquisition, and technical

laboratory support and training.

Acknowledgments

Figure 1.

One drawback to the using scanning

electron microscopy (SEM) is that it

operates under vacuum and in many

SEMs the samples must be rendered

conductive to be viewed. This is often

achieved by coating samples with a

very thin layer of palladium and gold

metal particles or carbon. However,

there are a number of different types of

SEMs which all have specific purposes,

often associated with additional pieces

of equipment like specialized stages or

collectors. Some of these do not require

dry or conductive samples.

Fundamentally and functionally,

electron microscopes are in many ways

analogous to their optical counterparts

(light microscopes: LM). This is

somewhat surprising at first glance,

given the contrast between the simple

technology of the LM and the complex

electronics, vacuum equipment, voltage

supplies and electron optics system of

electron microscopes.

Figure 2.

The formation of an image requires a

scanning system to construct the image

point-by-point and line-by-line. The

scanning system uses two pairs of

electromagnetic deflection coils (scan

coils) that scan the beam along a line

then displace the line position to the next

scan so that a rectangular raster

(represented here by a red circle

instead) is generated both on the

specimen and on the viewing screen.

The first pair of scan coils bends the

beam off the optical axis of the

microscope and the second pair bends

the beam back onto the axis at the pivot

point of the scan. In order to

produce contrast in the image the signal

intensity from the beam-specimen

interaction must be measured from

point-to-point across the sample surface.

Signals generated from the specimen

are collected by an electron detector,

converted to photons via a scintillator,

amplified in a photomultiplier, and

converted to electrical signals and used

to modulate the intensity of the image on

the viewing screen, seen in the different

shades of grey on images D and E.

Figure 3.

After inner shell ionization, the atom may relax by

emitting a Characteristic X-ray or an Auger

electron. The energy of the Auger electron is

related to the electronic configuration of the atom

that was ionized by the primary electron beam,

causing variation on the EDS spectrums seen in

images F and G.

The fluorescence yield is the relative yield or ratio

of X-rays to Auger electrons, elements in the

samples chemical composition and those hit with

x-rays. Elements with low ionization energies, i.e.

the lighter elements on the periodic table, have

low fluorescence yields. That is, when an inner

shell ionization occurs it is more likely that an

Auger electron will be produced rather than an X-

ray photon.

This principle and shells are illustrated above.

The intensities of X-ray peaks for elements of low

atomic number are smaller compared to those

with a higher fluorescence yield.

Ammrf.org.au (2014). Introduction | MyScope. http://www.ammrf.org.au/myscope/confocal/introduction/

X-ray Absorption:

Not all of the X-rays that are generated in the sample by the primary

electron beam are emitted from the sample. This is particularly true in the

SEM where X-rays are generated within the interactions at a depth of

many microns. X-rays may be absorbed by other elements in the sample

due to the photo-electric effect. This effect is the observation that many

metals emit electrons when light shines upon them. Electrons emitted in

this manner can be called photoelectrons. If the energy of an X-ray photon

is equal to the critical ionization energy of an electron in another element in

the sample then there is a high probability that the X-ray will be absorbed

and a photoelectron produced.

While the absorption of X-rays depends on the other elements present in

the sample, it is also true that low-energy X-rays are more likely to be

absorbed than those with higher energies, and elements with higher

atomic numbers tend to be strong absorbers of lower energy X-rays.

The length of the path that the X-ray travels through the sample will also

influence absorption. The longer the path length, the more likely it is that

the X-ray will be absorbed. Again, low-energy X-rays are more likely to be

affected by longer path lengths than higher energy X-rays.

Dividing one Bos taurus, one Equidae, and two Cervus elaphus bones were

sawed once each with a circulating, reciprocating, and hand saw creating

(n=16). Samples were prepared from sites of direct burning after five

minutes of incineration with average temperatures of 476.2◦C

recorded using a Digi-Sense thermocouple thermometer. Microscope

observations and images of kerf patterning were completed and compared

using light stereomicroscope and SEM. Energy dispersive X-ray analysis

(EDAX) or energy dispersive X-ray microanalysis (EDXMA) is an analytical

technique used for the elemental analysis and chemical characterization of

samples, also quantifying levels of chemical residues. These analyses can

vary depending on experimental and behavior manipulation like firing.