This document discusses various techniques used in metalworking and metallurgy, as well as their applications in crime detection. It describes processes like casting, forging, rolling, and machining that are used to shape metals. It then covers examining counterfeit coins and restoring erased serial numbers on metals. Specific chemical etching solutions and methods are provided for revealing erased marks on different metal alloys.

1. AS APPLIED TO CRIME DETECTION

2.  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

3.  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.

4. ROBBERY
THEFT
HIT-AND-RUN CASES
BOMB AND EXPLOSION
NAIL EXAMINATION
COUNTERFEIT COINS
RESTORATION OF SERAIL NUMBERS

5. 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

6. Example of a cast coin

7. 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

8. An example of Struck coins

9.  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.

10. 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.

11. 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.

12.  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.

13.  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.