forensic microscopy

ASCLD

American Society of Crime Laboratory Directors

ASCLD-LAB

ASCLD Lab Accreditation Board

ASTM

American Society for Testing and Materials, International

ISO

International Organization for Standardization

AAFS

America Academy of Forensic Sciences

IAI

International Association for Identification

AFTE

Association of Firearms and Toolmarks Examiners

ASQDE

American Society of Questioned Documents Examiners

SOFT-Tox

Society of Forensic Toxicologists

FEPAC

Forensic Education Programs Accreditation Commission

Evidence

Any information given in a legal investigation to make a fact or proposition more or less likely

Kinds of evidence

circumstantial, conclusive, conflicting, corroborating, derivative, exculpatory, foundational, hearsay, incriminating, presumptive, probative, rebuttal, tainted

Class

group of objects with similar characteristics

Individualization

classification of an object into a group with only one member - itself

Simple magnification

a single lens used to form an enlarged image of an object

Compound magnification system

magnification occurs in two stages

virtual image

the image the eye perceives and is visible only as a result of the compound magnification system

real image

image that can be seen on the screen

lens

a translucent material that bends light in a known and predictable manner

focal length

the distance between the two points of focus on either side of the lens

resolution

the minimum distance two objects can be separated and still be seen as two objects

eyepiece/ocular

the lens the observer looks into when viewing an object microscopically

monocular

microscope having one eyepiece

binocular

microscope having two eyepieces

field of view

area seen when looking through the eyepeice

objective

the lens in a microscope that is closest to the object being studied

numerical aperture

an angular measure of the lens's light-gathering ability

tube length

distance from the lowest part of the objective to the upper edge of the eyepiece

coverslips

the thin glass plates that are placed on top of mounted specimens, protect the specimen and the objective from damage

resolution equation

d\=wavelength of light / 2NA

numerical aperture equation

NA\= Nsin(u)
N \= RI of the medium between the coverslip and front lens
u \= half the angle of aperture of the objective

stage

platform where specimen sits during viewing

condenser

lenses below the stage that focus or condense the light onto the specimen field of view

condenser diaphragm

control to eliminate excess light and adjust for contrast in the image

field diaphragm

control that allow more or less light into the lens system

Kohler illumination

sets the light rays parallel throughout the system, allowing them to evenly illuminate the specimen

refractive index

relative speed at which light moves through a material with respect to its speed in a vacuum

refraction

bending of light

RI equation

N\=C / v
C\=2.998x10^8 m/s

Snell's law equation

N1sin(q1)\=N2sin(q2)
N\=RI
q\=angle of light traveling through the material with respect to the normal

Snell's law

the principle whereby light will pass into a boundary at an angle to the surface and be refracted

isotropic

materials that demonstrate the same optical properties in all directions - one RI

anisotropic

materials that have optical properties which vary throughout the material

polarizer

filter that orients light perpendicularly to the axis of the filter

analyzer

filter aligned opposite that of the polarizing filter; located above the objective

birefringence

the decomposition of light into at least two rays, ordinary and extraordinary, when it passes through anisotropic materials

birefringence equation

B\=Ne-No
N\=RI of Extraordinary and Ordinary rays

retardation

difference in velocity of the ordinary and extraordinary rays

retardation equation

r\=t(N2-N1)
t\=thickness
N2-N1\=B

fluorescence

luminescence of a substance excited by radiation

phosphorescence

long-lived emission, and fluorescence, in which the emission stops when the excitation stops

wavelength

distance between corresponding points on two adjacent waves

frequency

number of waves that pass a given point in one second

epidermis

outer layer of skin from which hair grows

hairs

fibrous growths that originate from the skin

follicle

structure in the epidermis within which hairs grow; roughly cylindrical tube with a larger pit at the bottom

keratin

tough protein-based material from which hair, nails, and horns are made in animals

sebaceous glads

glands that produce oils to coat hairs, helping to keep them soft and pliable

anagen

actively growing phase in which a hair follicle produces new cells and pushes them up the hair shaft as they become incorporated into the structure of the hair

pigment

small colored granules that give hairs their particular color

catagen

phase after active growth where the hair transitions into a resting phase, the follicle begins to shut down production of cells, the cells begin to shrink, and the root condenses into a bulb-shaped structure

telogen

resting phase for the follicle in hair growth where the cell production has ceased completely

imbricate

scale pattern in human hair

cuticle

series of overlapping layers of scales on the outside of a hair that form a protective covering

cortex

makes up the bulk of the hair structure

pigment granules

granules that vary in size, shape, aggregation, and distribution throughout the cortex of hair

cortical fusi

small bubbles of various sizes and shapes that may appear in the cortex of hair

ovoid bodies

structures that look like very large pigment granules which may appear irregularly in the cortex of hair

denier

weight in grams of 9,000 meters of fibrous material

warp yarns

yarns that run lengthwise to the fabric

weft yarns

yarns that run crosswise

natural fibers

flax, jute, ramie, hemp, sisal, abaca, cotton, kapok, coir

becke line

a thin bright line that appears at the margin between a liquid mount and a translucent sample of different refractive indices

dye

organic chemical that is able to absorb and reflect certain wavelengths of visible light

glass

an amorphous solid with properties of both a solid and a liquid

float glass

type of glass made by pouring molten glass onto a bed of molten tin so that the surface is very flat

soda-lime glass

glass doped with calcium oxide and sodium carbonate

borosilicate glass

glass doped with boron oxide; very resistant to rapid heating and cooling

tempered glass

glass made by rapid heating and cooling to induce tiny cracks on its surface so it will form round balls if it breaks

paint

a suspension of pigments and additives intended to color or protect a surface

microtome

a mini-vice that holds a sample in place while a heavy and very sharp glass or diamond-edged knife slices off sections a few tens of microns thick

batch lot

a unit of production and sampling that contains a set of analytically indistinguishable products

Bertillonage

a complex system of anthropometric measurements, photographs, and a detailed description used to assist police in identifying criminals

primary friction ridges

friction ridges that develop deep in the dermal layer of the skin and begin forming in the ninth or tenth week of fetal development

secondary friction ridges

friction ridges that develop from week 17 and mature by week 24 of fetal development

patent prints

prints that are visible without further development; may be from transferred materials, like blood, or impressed into a material, like clay, fresh paint, or putty

latent prints

prints composed of the sweat and oils of the body that are transferred from the ridge pattern to some substrate where they persist for some time until found by one of numerous visualizing techniques

fingerprint powder

a print visualizing technique that used finely ground colored, fluorescent, or magnetic materials, which are brushed lightly over a suspected print to produce contrast between the background and the now-visible print

minutiae

the kind, number, and location of various friction ridge characteristics as points of comparison in fingerprint examinations

AFIS

Automated Fingerprint Identification Systems

Level 1 detail

a primary fingerprint classification that includes the general ridge flow and pattern configuration

Level 2 detail

a primary fingerprint classification that includes formations, defined as a ridge endings, bifurcations, dots, or combinations of these features

Level 3 detail

a primary fingerprint classification that includes all attributes of a ridge, such as ridge path deviation, width, shape, pores, edge contour, incipient ridges, breaks, creases, scars, and other permanent minutiae

requested writings

samples of known handwriting that have been requested and specified by the document examiner

exemplars

known or authentic writing or printing samples

non-requested writing

a sample of known handwriting that existed before the case; usually a business or personal document that is known to have been written by the subject

formal signature

a signature on an official document such as a will

informal signature

a signature written on routine correspondence such as a personal letter

stylistic signature

a signature used in signing checks, credit card receipts, etc; very individual and may bear little resemblance to a formal or informal signature

obliteration

overwriting of handwriting with another writing instrument