Presentation1

AS APPLIED TO CRIME DETECTION

Metallurgy is art of extracting and working

in metals by application of chemical and

physical knowledge.

Metallography is the branch of metallurgy

which involves study of the microstructures

of metal and alloys.

DEFINITION

Main article: Metalworking

Metals are shaped by processes such as:

casting – molten metal is poured into a shaped mold.

forging – a red-hot billet is hammered into shape.

flow forming

rolling – a billet is passed through successively narrower rollers to create a sheet.

laser cladding – metallic powder is blown through a movable laser beam (e.g. mounted on a NC 5-axis

machine). The resulting melted metal reaches a substrate to form a melt pool. By moving the laser head, it

is possible to stack the tracks and build up a three-dimensional piece.

extrusion – a hot and malleable metal is forced under pressure through a die, which shapes it before it

cools.

sintering – a powdered metal is heated in a non-oxidizing environment after being compressed into a die.

metalworking

machining – lathes, milling machines, and drills cut the cold metal to shape.

fabrication – sheets of metal are cut with guillotines or gas cutters and bent and welded into structural

shape.

Cold-working processes, in which the product’s shape is altered by rolling, fabrication or other processes

while the product is cold, can increase the strength of the product by a process called work hardening.

Work hardening creates microscopic defects in the metal, which resist further changes of shape.

ROBBERY

THEFT

HIT-AND-RUN CASES

BOMB AND EXPLOSION

NAIL EXAMINATION

COUNTERFEIT COINS

RESTORATION OF SERAIL NUMBERS

CAST COINS- are made in one operation by the metal in molds prepared by taking impressions of genuine coins in suitable materials such as plaster of Paris, clay of even bronze.

Characteristic of Coin• poor imitations• surface of cast coin is uneven• edges of lettering and design are rounded

instead of sharp

Example of a cast coin

STRUCK COINS – are often well executed

and their detection id not an easy matter

since the weight, size, specific gravity,

milling and composition may all be good.

COUNTERFEIT COINS

An example of Struck coins

In examining counterfeit coins whether cast or struck, the most important points consider are the detail and the design and the manner in which this has been executed the milling, the beading on the inner side of the rim of the coin, color, weight specific gravity the determination of the hardiness of a coin, usually made by biting it, is not more of an assistance in a examination.

The ring of the coin is also for very little value since many counterfeit ring well while genuine, if cracked, ring badly.

The examination if the milling of a coin includes the determination of the number of ridge which is done by the coloring the edge of the coin by means of a pad moistened with aniline ink, then carefully removing the color of one of the ridges and then taking the impression of the circumstances of the coin on paper. Starting from the blank ridge count the number of lines made by the ridges. The number of lines counted plus one is the number of the ridges of the coin. Attention is however invited to the fact that the diameter of genuine coins of the same denomination from the dame mint may vary with different issues of coins and naturally, the number of ridges will also vary.

The principle involved in the restoration of numbers is an

follows: when a number or any mark is stamped on

metal, the crystalline structure of the metal in the metal in

the neighborhood of the stamp is disturbed. This

substance penetrates to an appreciable distance into the

substance of the metal , but is not visible to the naked

eye one the actual identations caused by the punch have

been removed. However, when etching fluids are applied

to this surface, the disturbed or strained particles of the

metal differ in the rate of solubility makes it possible, in

many cases.

Chief Technician of the crime laboratory of Indiana state

Police described a simple unexpensive method of electro –

acid etching of eradicated numbers.

An ordinary flashlight battery may be used to supply the electric

current solder an alligator champ to a piece of wire about 12 inches

long, this wire will ground the circuit to the metal to be etched. The

ground wire goes positive to the pole of the battery. Another wire about

12 inches long is attached to the cotton swab by negative pole of the

battery, and the current will flow when the swab is touched to the

metal. The battery may be held in place by means of a metal holder or

clamp which will permit contract at the terminals.

Cast iron and cast steel- 10% solution of sulfuric acid and potassium dichromate Wrought iron and forged irons and steels- solution 1. Hydrochloric acid 80 cc. , copper

chloride, 12.9 gms. , alcohol, 50 cc, Solution 2. 15 % nitric acid. The method is to apply with a swab a little of the acid copper chloride solution (solution 1). Dry with cotton and then apply solution 2. Alternate the swabbing until the numbers appear.

Aluminum- Glycerine, 30 cc. hydrofluoric acid, 20 cc, nitric acid 10 cc to the dangerous nature of hydrofluoric acid, only experienced chemist should use the solution. Another formula is Copper chloride, 200 gms. , hydrochloric acid, 5 cc., and water 1000 cc.

Stainless steel- use dilute sulfuric acid or 10% hydrochloric acid in alcohol. Lead- Glacial acetic acid, 3 parts, hydrogen peroxide, 1 part. Zinc- 10% sodium hydroxide solution. German silver- Ferric chloride syrupy solution, 25% conc. Hydrochloric acid, 25% and water

50%. Tin- 10% hydrochloric acid. Silver- concentrated nitric acid solution. Gold and platinum- Aqua regia. Wood- erased numbers and figures on wood can also be treated and excellent results have

been obtained by suspecting the suspected areas o t a jet of steam. Copper brass, German silver , and other copper alloys – Ferric chloride, 19 gms.,

hydrochloric acid, 6 cc. and 100 cc.Retaining wall method should employed.

The Technical Laboratory of the FBI recommends the use of the magnetic particle method when working on magnetic metals.

Etching : An artistic print made from a plate on which the

artist has etched a design with acid.

Swab : a bit of sponge, cloth, cotton, or the like,

sometimes fixed to a stick, for cleansing the mouth of a

sick person or for applying medicaments, drying areas,

etc.