ABSTRACT

Glitter is frequently encountered as transfer evidence (trace or associative evidence) in
those crimes where there is intimate contact between assailant and victim. The transfer of cosmetic glitter to airbags in vehicle accidents may also help to show the seating positions of drivers and passengers. Glitter particles from different sources exhibit great variety. The more ways a questioned glitter particle may be characterized and compared with glitter from a known source,
the smaller the subclass it will fall into and thus the greater its value as trace evidence. Many manufacturers of glitter include a product line described as “holographic glitter.” Holographic glitter achieves its color effects by virtue of regularly-spaced striae (gratings). These are not on the outer surface but instead are covered by a thin clear protective polymer layer.
This article will illustrate how these striae may be detected, documented, and the striae spacing measured using light microscopy.

 

 

INTRODUCTION

Glitter has been previously reported as
trace evidence and various methods for its characterization described (1-8).
One immediately thinks of color, shape, and size. Shape and size are no
problem, but color determination turns out to be quite complex. A thorough
discussion of the science behind the perception of color as it applies to
glitter particles is beyond the scope of this paper, but color in glitter
particles is achieved based more on the principles of the optics branch of
physics than through chemistry (dyes and pigments).

 

World-wide, there are well over a dozen
different manufacturers of glitter. Many of these manufacturers offer a
subclass described as holographic glitter. The determination that one or more
questioned glitter particles fall into this subclass and the determination of
their properties within the subclass can help discriminate between similar
glitter particles and thereby greatly increase their potential value as
associative evidence. The prismatic effect of holographic glitter is achieved
through the interaction of light with gratings (parallel, evenly spaced fine striations
just under a clear protective polymer layer on the surface of the glitter
particle).  These striations may be seen in the photomicrograph in Figure 1.
The determination that a questioned glitter particle is of the holographic type,
and the measurement of the distance between striae may help to place the
particle into a smaller subclass. Because the grating is not actually on the
particle surface, the greater depth of field at higher magnification afforded
by scanning electron microscopy is of no avail. This article will show that
these gratings can be seen and the striae spacing used for the questioned and
known particles compared using light microscopy at about 1000x.




Figure 1.

Surface of two different glitter
particles illustrating an ~ 0.5 micrometer (left) and ~ 1.0 micrometer diffraction
grating (right).  Top is a stage micrometer with lines 10 micrometers apart.
Meadowbrook Inventions, Alpha Jewels HTMP, silver, .008” x 0.008” (right), and
Alpha Jewels, silver, 0.025” hexagonal (left).  Conditions: Mounted in PermountTM
under a cover glass, 60X dry objective with 0.80 NA and 6.7X photo eyepiece.
[Photomicrographs by Edwin Jones, Ventura County (California) Sheriff’s
Department Forensic Sciences Laboratory. Used with permission from Figure
1-5, Chapter 1, FORENSIC ANALYSIS ON THE CUTTING EDGE: New Methods for Trace
Evidence Analysis
, (2007) Robert D. Blackledge, Editor, Wiley Interscience,
Hoboken, New Jersey.]

 

METHODS

All glitter particles examined in this study were purchased from Meadowbrook Inventions, Inc., 260 Minebrook Road, Bernardsville, NJ 07924-0960, USA (www.meadowbrookinventions.com). All were
either from their product line Alpha Jewels HTMP or Alpha Jewels. They describe
Alpha Jewels HTMP as “Precision cut Holographic Glitter particles
consisting of Micro-embossed Aluminum particles designed for applications requiring
Prismatic Special Effect with excellent Heat Resistance.” Alpha Jewels are
described as “Precision cut Holographic Glitter particles consisting of
micro-embossed vacuumed metalized (0.5% aluminum) polyethylene terephthalate,
designed for applications requiring Prismatic Special Effect with excellent
fastness properties. Solvent Resistant.” Alpha Jewels HTMP are further
described as having a thickness of 0.001″ (25 micrometers) and a specific
gravity of 2.4, with the Alpha Jewels having a thickness of 0.002″ (50
micrometers) and a specific gravity of 1.4. Alpha Jewels are offered in the
following six colors: Silver, Gold, Strato Blue, Pink, Ocean Green, and
Lavender. They are offered as square particles  0.008″ along a side;
rectangular particles 0.035″ x 0.004″, 0.062″ x .0125″, or
0.125″ x 0.0125″, as hexagonal particles 0.008″ (one apex to
opposite apex), 0.015″, 0.025″, 0.040″, 0.062″, and 0.094″.
Also, specialized shapes are available as 1/8″ stars, hearts, or diamonds.

 

In this study the following 12 glitter products were examined:

 

Sample #001 Alpha Jewels HTMP Silver 0.008″ x 0.008″ (Figures 2a-2d)

Sample #002 Alpha Jewels HTMP Silver 0.025″ hexagonal

Sample #003 Alpha Jewels Silver 0.008″ x 0.008″

Sample #004 Alpha Jewels Silver 0.025″ hexagonal

Sample #005 Alpha Jewels Gold 0.008″ x 0.008″

Sample #006 Alpha Jewels Gold 0.025″ hexagonal

Sample #007 Alpha Jewels Strato Blue 0.008″ x 0.008″

Sample #008 Alpha Jewels Strato Blue 0.025″ hexagonal

Sample #009 Alpha Jewels Pink 0.008″ x 0.008″

Sample #010 Alpha Jewels Pink 0.025″ hexagonal

Sample #011 Alpha Jewels Ocean Green 0.008″ x .008″

Sample #012 Alpha Jewels Ocean Green 0.025″ hexagonal

 

[Sample numbers are not Meadowbrook Inventions numbers but were used by the authors in previous
studies. Correspondingly numbered small samples were issued to the attendees at
a workshop on glitter presented on 13 August 2007 in Clearwater Beach, Florida as part of a Trace Evidence Symposium sponsored
by the National Institute of Justice and the Federal Bureau of Investigation.]

 

Glitter photos settings: The samples were
prepared by dry mounting a small sample of glitter on a standard glass slide
with no coverglass.  The images were viewed with a Nikon MM-40 measuring
microscope equipped with LU Plan objectives [5x (0.15 NA), 50x (0.55 NA), and
100x (0.80 NA)].  Illumination used standard tungsten bulb, reflected
brightfield condition, no neutral density or polarizing filters were inserted in the light
path.  Photographs were taken with a SPOT-RT color CCD camera (model 2.2.1.)
and SPOT version 4.7 software set on auto gain and auto exposure.  Micrometer
markers in the photographs were calibrated against a MicroRuler MR-1 (s/n 5-14)
size reference standard.

RESULTS & DISCUSSION

As seen in Figures 2 through 13 each of the
twelve samples were viewed at three magnifications, 50x, 500x, and 1000x. This
was done to illustrate that the gratings producing the prismatic effects can
usually not be seen at low magnification. Although with some samples they can
be seen at 500x, with many they are only clearly seen at 1000x. Parallel fine
lines or scratches can be seen with many samples at 500x, but these are not
evenly spaced nor are they parallel to the striae seen at 1000x. The parallel
unevenly spaced scratches seen at 500x are surface scratches while the evenly
spaced striations that produce the holographic effect are embossed on a vapor
deposited aluminum layer that has over it a thin clear protective polymer
layer. Glitter is cut from rolls of multilayered film. As with synthetic
fibers, these thin sheets of multilayered film are produced by an extrusion
process. In this process the extruded sheets pass over a series of rollers.
Although just supposition at this point, the parallel but unevenly spaced lines
or scratches seen at lower magnifications may be the result of the film passing
over various rollers. If this were true, these lines seen at lower
magnification could indicate the machine direction of the film before it is cut
into glitter. As with synthetic fibers, this extrusion process imparts a
partial crystalline nature so that refractive index with the machine direction
may be different than across the machine direction. If questioned and known
glitter particles are compared between crossed polarizers using a polarizing light microscope (PLM),
it is important to bear in mind that glitter particles have two sides
and that for meaningful comparison you must be comparing the same sides and the
machine direction of the two when compared must be parallel.

 

 

REFERENCES

  1. Grieve, M.C. (1987) Glitter particles – an unusual source of trace evidence? Journal of the
    Forensic Science Society, 27:405-412.
  2. Aardahl, K., Kirkowski, S., and Blackledge, R.D. (2005) A target glitter study.
    Science & Justice, 45:7-12.
  3. Blackledge, R.D. and Jones, E.L. Jr. (2007) All that Glitters Is Gold!. Chapter
    1, 1-32, in FORENSIC ANALYSIS ON THE CUTTING EDGE: New Methods for Trace
    Evidence Analysis, Robert D. Blackledge, Editor, Wiley Interscience, Hoboken, New Jersey.
  4. Aardahl, K. (2003) Evidential value of glitter particle trace evidence, Masters
    Thesis, National University, San Diego, California.
  5. Kirkowski, S., (2003) The forensic characterization of cosmetic glitter
    particles, Masters Thesis, National University, San Diego, California.
  6. Weber, C., (2004) Glitter as trace evidence, Masters Thesis, National University, San Diego, California.
  7. Siciliano, M.A. (2006) Glitter as associative evidence: determination of
    individual particle thickness and density, Masters Thesis, National University, San Diego, California.
  8. Blackledge, R.D. (2007) Glitter as Forensic Evidence, Trace Evidence Symposium
    sponsored by the NIJ and the FBI, Clearwater Beach, Florida [Available on the
    Internet at: http://projects.nfstc.org/trace/docs/final/Blackledge_Glitter.pdf ]

FIGURES

Sample #001 Alpha Jewels HTMP Silver 0.008″ x 0.008″



Figure 2a: Sample 001-50x


Figure 2b: Sample 001-500x


Figure 2c: Sample 001-1000x


Figure 2d: Sample 001-1000x
(Cropped from Figure 2c)

Sample #002 Alpha Jewels HTMP Silver 0.025″ hexagonal



Figure 3a: Sample 002-50x


Figure 3b: Sample 002-500x


Figure 3c: Sample 002-1000x



Figure 4a: Sample 003-50x


Figure 4b: Sample 003-500x


Figure 4c: Sample 003-1000x

 



Figure 5a: Sample 004-50x


Figure 5b: Sample 004-500x


Figure 5c: Sample 004-1000x

 



Figure 6a: Sample 005-50x


Figure 6b: Sample 005-500x


Figure 6c: Sample 005-1000x

 



Figure 7a: Sample 006-50x


Figure 7b: Sample 006-500x


Figure 7c: Sample 006-1000x

 



Figure 8a: Sample 007-50x


Figure 8b: Sample 007-500x


Figure 8c: Sample 007-1000x



Figure 9a: Sample 008-50x


Figure 9b: Sample 008-500x


Figure 9c: Sample 008-1000x

 



Figure 10a: Sample 009-50x


Figure 10b: Sample 009-500x


Figure 10c: Sample 009-1000x

 



Figure 11a: Sample 010-50x


Figure 11b: Sample 010-500x


Figure 11c: Sample 010-1000x

 



Figure 12a: Sample 011-50x


Figure 12b: Sample 011-500x


Figure 12c: Sample 011-1000x

 



Figure 13a: Sample 012-50x


Figure 13b: Sample 012-500x


Figure 13c: Sample 012-1000x