Microscopy Exam 2 Review

Isotropic

Materials exhibiting the same optical properties in all directions.

Anisotropic

Materials with varying optical properties in different directions.

Pleochroism

The phenomenon where a substance displays different colors when viewed from different angles under polarized light.

Birefringence

The difference between two principal refractive indices in a material.

Double Refraction

The splitting of light into two rays traveling at different speeds through certain materials.

Orthoscopic

Distortion-free view using parallel rays in optical mineralogy.

Conoscopic

Refers to a cone of converging rays of light in optical mineralogy.

Optic Sign

Determined by the orientation of the E and O rays; positive if E > O, negative if E < O.

positive and negative, blue in quadrant 1 and 3 is positive, yellow in 1 and 3 is negative.

most fibers are positive except some acrylics and triacetate

Sign of Elongation

Indicates if the direction of the crystal length corresponds to the high or low index direction; positive for high index, negative for low index.

Tobi's Method

A method for relating the angular aperture and axial angles in optical mineralogy.

Spindle Stage

A device used to hold a crystal for rotation to observe optical properties.

Excalibr

A tool used to upload points of extinction while rotating a crystal.

Monochromatic Interference Contrast (DIC)

A microscopy technique that enhances contrast in transparent specimens by using polarized light, allowing for detailed imaging of structures without staining.

polarized monochromatic light may be extinguished by the analyzer after passing through an anisotropic mineral

Dispersion Staining

A technique that utilizes a central and an annular stop to produce identifying colors.

Cotton Characteristics

• (Incomplete Extinction, Spiral Structure, Lumen, Undulation, Amber Retardation Color)

• incomplete extinction: lack of an extinction position. As the stage is rotated between crossed linear polarizing filters the fiber's brightness doesn't significantly change.

• Lumen: the hollow canal that runs the length of the fiber

Weave Fabric Construction

Different weaving techniques including plain, twill, and satin.

Plain Weave

The simplest weave in which the weft (crosswise) yarn is passed over then under each warp (lengthwise) yarn.

Twill Weave

a textile weave in which threads are crossed over one another to give an appearance of diagonal lines.

Satin Weave

A weave that produces a smooth, shiny-surfaced fabric resulting from passing the weft yarn over and under numerous warp yarns to create long floats.

Fiber Shapes (x-section vs longitudinal)

(Cylindrical, triloba (carpet fiber)l, dogbone or dumbbell, multiserrated)

Undulation in Fibers

The twist of natural fibers identified as 'S' or 'Z'.

Optic Angle

Tobi's method-relationship between angular aperture; axial angles 2E, 2H, and 2V; and linear diameters of the back focal plane of the objective.

Crystal Formatting

Crystals can be classified into isotropic (cubic) and anisotropic systems (uniaxial and biaxial).

Understanding these systems is essential for identifying minerals and predicting their behavior under polarized light.

Uniaxial Anisotropic

crystals include tetragonal, hexagonal, and rhombohedral systems, which exhibit unique interference figures.

Biaxial Anisotropic

crystals consist of orthorhombic, monoclinic, and triclinic systems, each with distinct optical properties.

Crystal Morphology

can be categorized into equant, columnar, tabular shapes, and those with constant face angles.

Retardation

calculated using the formula: birefringence x thickness x 1000 (to convert from nanometers to microns).

Isotropism

materials exhibiting the same optical properties in all directions, appearing dark under crossed polars in PLM.

Anisotrpism

indicates materials with varying properties in different directions, which do not go to extinction under crossed polars, remaining visible as the stage rotates.

Calcite Rhomb (Icelandic Spar)

two dots, one moves around the other and they appear to be on different levels. When using polaroid, one dot disappears. When two are moved together, film turns entirely dark when positioned in a certain way different heights because different values of refractive indices.

Starch Grains ID

Maltese Cross pattern

Cellulose down in particular order

Parallel, Oblique, Symmetrical Extinction

• 0 degrees (“goes extinct”)

• 45 degrees

  • Those that don’t go extinct a little off 0 degrees

• other angles

  • Goes extinct when symmetrical

Isotropic Indicatrix

• a sphere

• can be placed anywhere within or on a crystal so long as the crystallographic directions are moved parallel to themselves.

• Three dimensional plot of refractive index vs vibrational direction

Uniaxial Indicatrix Figures

• (Oblate or Prolate Ellipsoids of Revolution)

• 3 central sections: principal, circular, and random

• Positive (prolate; vertical oval) and negative (oblate; horizontal oval)

Biaxial Indicatrix Figures 

• (Triaxial Ellipsoids)

• Three axes: x,y,z

• Three dimensional plot of refractive index vs vibrational direction

Uniaxial and Biaxial Interference Figures

• cross with yellow and blue quadrants, cross doesn't disappear when moved.

  • Positive if E >O-> Blue in quadrants 1 and 3=additive

  • Negative if E<O-> Yellow is in 1&3

Color temperature

2000k-8000k candlelight to snow, water, and blue sky

“w” or “o” ray, “E” or “e” ray

calcite rhomb rays, ordinary ray (predictable path) and extraordinary ray (obvious contradiction of snell's law).

O and E ray vibrate perpendicular to each other

“a” -alpha, “B” -beta, “Y” -gamma rays

slow rays parallel, additive compensator

subtractive compensator

Phase Contrast Microscopy (PCM)

A contrast technique in which the phase position of the non-diffracted light is shifted in relation to the diffracted wave fronts, thereby improving the constructive and destructive interference conditions.

typically used for glass chips and semen

phase plate -> objective -> Condenser-> light ring

(“Hoffman”) Modulation Contrast

Modulator->Objective->condenser->slit

A Slit allows light to come in at oblique angle so one side of image is bright and the other is dark.

Bright Field Microscopy

produces an image made from light that is transmitted through a specimen against a light background

Dark Field Microscopy

shows the specimen against a dark background and provides good resolution

Central-Stop D.S. and Annual Stop D.S.

(The two stops produce complimentary colors).

the particles and immersion liquids must have different dispersion curves which intersect sharply in the visible light region

Differential Interference Contrast (DIC)

microscope that uses a prism to split the incident beam into two mutually perpendicular components.

analyzer makes the vibration directions parallel so light rays can interfere at the intermediate image plane.

Wayne Williams Case

tried for the murder of two individuals in the Atlanta, Georgia

An essential part of the government's case was the numerous fibers linking Williams to the murders

yellow-green fibers discovered on a number of the murder victims were linked to a carpet in the Williams home which helped proved his guilt

Put Fiber forensic evidence on the map

Behavioral analysts/profiling

Vegetable Fibers

seed hairs - cotton, kapok

-Bast or Stem Fiber- (ie; Linen, Manila, Hemp)

-Trichomes or Leaf hairs- (ie; Cannabis sativa)

unicellular and used as individual fibers rather than bundles.wool, silk, fur or domesticated

Animal Fibers

Wool-(Important textile)

Silk- (From Silkworm Bombyx mori)

Other Animal Fibers (Furs, Domesticated

Mineral fibers

Asbestos

Bast fibers

Jute, Ramie, Sisal, Hemp

Marijuana ID by leaf fibers 

(Crystalith hairs (bear claw), conical trichomes (long hair), glandular hairs(where THC is))

In the old days

3 botanical structures (see above)

Positive levine test (THC test)

Modified Herzog test

an empirical test for determining the fibrillar orientation using polarized light microscopy.

Old way of identifying natural fibers

Synthetic fibers

Nylons, polyesters, polyolefins, polyethylenes and polyproyplenes, acrylics, saran, vinyon, elastic, glass, metallic

Regenerated fibers

Rayon, Acetates

Monomers

building blocks of polymers glucose

Polymers (“poly-glucose”) 

(cellulose, rayon)

Delustering agents

• reduces the sheen of synthetic fibers.

• Back in my day 

  • a polyester suit got shiny looking after a few days and gross. 

  • Let's try wool instead. 

  • Pigment in the hair shaft. 

  • Add pigment in synthetic Fiber. 

  • Titanium dioxide (cheap) put into polymer makes it look better

Complete extinction (synthetic fibers)

man-made fibers and silk show complete extinction unless they have been deformed.

Low birefringence (acrylics, acetates)

modacrylic, acetate, acrylic, triacetate

Moderate birefringence

(Olefins, Nylon)

(cellose)

High birefringence

Polyester

Cross-striations

bast fibers-dislocated fibrils

shown between crosses polars, because of dislocation of fibrils during bending.

Weaves, knits, felts

Fabric construction

Felt (non woven) - common in cars, tyvek suit

Weaving: plain, twill, satin

Warp and weft or fill

components used in weaving to turn thread into fabric

Cordage terminology (plys, strands, yarns, fibers)

• Look at twisting

• Rope made up of plys (first division)

• Then strands

• Strands made up of yarns

• Yarns made up of fibers

• Sometimes core (helps it not fray as much)

“S” or “Z” twist of cordage

Affects optical properties

Silk-bombyx mori (looks synthetic)

Silk from a moth

See Textile Analytical Scheme

Optic sign of elongation

(Most fibers are positive except for some acrylics and some acetates)

What’s a fiber that has a lot of fibrils or opemits and has a lot of dislocations? 

Bast Fiber

What is a fiber that is very luxurious that almost looks synthetic but is not?

Silk fiber

This fiber undulates, incomplete extinction, amber retardation color and lumen:

Cotton

Authors of textbook

McCrone, Delly, Bloss, Bell, Morris