Climate Change Impacts on Terrestrial and Aquatic Ecosystems.pptx
TOOL MARKS
1. TOOL MARKS
SUBMITTED TO :-
Ms. ARCHANA PATHAK MAM
BY :-
ASHLESHA S RATNAPARKHI
MSc FORENSIC SCIENNCE
1st YEAR
2. TOOL MARKS :-
A Tool mark is defined as the mark left by the forcible contact of
any implement such as a Screwdriver, Hammer, Saw, Drilling
Machine, Wrench, etc, with a softer surface.
These are found in cases like Robbery, Hit and Run, etc and are
forensically significant due to its individuality, permanency and
also helps to link the criminal with the crime scene and also aids in
the reconstruction of crime scene.
The nature and quality of a tool mark can be determined by :-
Relative hardness,
The magnitude of force applied,
The relative motion of one surface over the other.
3. TYPES OF TOOL MARKS :-
Tool marks are of four types namely,
1. Compression marks / Impressed marks :- These are produced when
a tool strikes the surface with pressure.
2. Striated marks :- These are produced when a tool scrapes the
surface.
3. Combination of Compression and Striated marks :- These marks as
the name suggests are the combination of compression and striated
marks.
4. Repetitive marks/ Multistroke marks :- These are produced when a
tool strikes the surface a number of times.
4.
5. CHARACTERISTICS OF TOOL
MARKS
The features of tool marks can be divided into three types as :-
Class characteristics :- These are the features produced by similar type
of tools.
Sub-class characteristics :- These are the features produced by tools of
same type that are manufactured on the same machine.
Individual characteristics :- These are developed by a tool while in use
due to wear and tear. No two tools can produce identical random
individual marks.
6. COLLECTION & EXAMINATION
OF TOOL MARKS
The following procedure should be adopted for collection and
examination of Tool marks :-
Photography :-
Tool marks should be photographed and at least two photos should be
taken, one showing the background with the impression and another a
close up of the impression.Scale should always be used while taking
photos and the camera should be kept perpendicular to the surface of the
tool mark.More details of the mark can be obtained by using oblique
illumination.
Tracing :-
Tool marks can be traced on a tracing paper as it helps in comparing the
class characteristics.
7. Lifting of tool marks :-
A cast or mould is simply a reverse or negative 3D image of an
impression. The following materials are generally used for making a
mould of a tool mark.
Plastic/rubber :-
It is used for lifting fine details of a tool mark.A lump of material is
softened by pressing in fingers and then applied on the surface.It is
pressed carefully as it is likely to be disturbed by out side pressure.
Dental casting materials can also be used as it also gives fine details of
tool marks.
Plaster of Paris :-
For large sized impressions Plaster of Paris which is partly hydrated
calcium sulphate , (CaSO4)2 1/2 H2O is used.
8. Metal casting :-
The mould of tool mark can also be made by metal casting. The suitable
metal for this purpose is known as Woods metal.This is a metal of low
melting point (71oC), which is suitable for casting tool marks.Its
composition by weight is Bismuth 50%, Lead 25%, Tin 12.5% and Cadmium
12.5%.
Cellulose acetate :-
Tool marks from stone, concrete, wood, etc. can be lifted by cellulose acetate
dissolved in acetone. A layer of 1/16 inch is made. However the cellulose
acetate cast should be photographed, with scale, immediately otherwise the
layer is likely to shrink.
9. RESTORATION OF TOOL
MARKS
Manufacture of valuable items, like automobiles, bicycles, firearms,
watches, etc., often register serial numbers on their product as means of
identification or to establish ownership. When criminals steal such
property they may attempt to alter or erase the identification marks by
either, filing the surface bearing marks or removing the marks by using
sandpaper or a grinding wheel.
But it is almost impossible to alter such marks without leaving obvious
evidence of an attempted erasure and hence can be restored and
analysed.
10. PRINCIPLE OF RESTORATION :-
Serial numbers are usually stamped on a metal body or frame or
on a plate with hard steel dies, and due to this the crystalline
microstructure of the metal gets compressed & strained.
When a suitable chemical reagent is applied, the strained &
unstrained areas will dissolve the metal at different rate.
This unequal rate of dissolution, of strained & unstrained
metal, helps in bringing out the original numbers.
11. Types of marks found on the vehicle parts and
other articles :-
1. CAST MARKS :- These marks are raised above the surface of
metal, but sometimes cast marks may sink into the metal
surface. However if these marks are erased, it is impossible to
restore them.
2. ENGRAVED MARKS :- These are of two types namely, marks
engraved by using chisel, and those made with an electric
engraver. If marks made by chisel or engravers are obliterated,
it can be restored provided the erasure is not too deep.
12. 3. PUNCHED MARKS :- Majority of articles bear serial numbers,
which are obtained by striking the metal surface with a die bearing
the marks in relief. The die is forcibly hammered into the metal,
which results in compression of the metal causing disturbance of
the surface underlying it. Erased punched marks of these types can
often be restored.
Punched
marks
Engraved marks
Cast marks
13. Methods Used to Obliterate Identification
Marks :-
1. Filing /grinding :- The original number would have been
filed away or ground with a power grinder followed by
polishing and then over stamping with a new number.
2. Peening :- This involves hammering the surface with a round
punch to hide the number.
3. Over stamping :- Here a new number is simply stamped over
the old. For numbers with curved surfaces i.e. 2,3,5,6,9 and 0,
the stamp 8 is the one most often chosen. For numbers with
straight surfaces i.e. 1 and 7, the stamp 4 is the obvious
choice. Serial numbers with a preponderance of ‘8’ or ‘4’
numbers should be treated with suspicion.
14. 4. Centre punching :- The surface bearing number is obliterated
with a pointed punch.
5. Substitution :- Substitution of an iron plate with a new number
over the original surface by pasting or welding.
6. Drilling :- It removes the number and the surrounding metal with
a drill. The cavity is usually filled up with either lead solder or
welding material.
7. Welding :- Heating the surface with either an oxy-acetylene
welder or an arc -welder until the metal flows.
Occasionally an original finish would be given to a previous
obliterated number surface
15. 1. The technique of applying the reagent is the same
for almost all metals.
2. Before treatment with chemical reagent, the
obliterated surface must be thoroughly cleaned of
dirt and greasy matter or paint with suitable
solvent like acetone or benzene & photographed.
3. The reagent is then applied to this surface with a
cotton ball, attached to a stick or glass rod.
4. The number is read under suitably adjusted
illumination. As soon as number appears a
photograph of entire item should be taken along
with close-up snaps because it may disappear after
subsequent application of the reagent.
16. Etching Reagents used on different surfaces :-
1. Steel surfaces (chassis and engine of cars, guns, gas cylinders etc) :-
Solution 1 (Fry’s reagent) - Crystalline cupric chloride (90gms),
Concentrated hydrochloric acid (120ml), Water (100ml)
OR
Hydrochloric acid (80ml),Water(60 ml),Copper
Chloride (12.9gms), Alcohol (50 ml).
Solution 2 - 15 % Nitric acid.
Apply the Solution 1 by swabbing the surface for 2-3 minutes with
cotton wool dipped in the reagent. Look for any digits revealed and
record it. Clean the surface with acetone (not water) and examine again.
Apply Solution 2 by swabbing the surface for approximately 1 minute
with cotton wool dipped in this solution. Look for any digits revealed
and record these.
17. 2. Copper, Brass, German Silver and other Copper Alloys :-
Ferric Chloride(19 gm),Hydrochloric acid(6 ml),Water(100 ml)
Apply the reagent as a swab until the number appears. When the reagent
is slow to develop the erased mark, form a wall of plasticine around the
erased mark. Use the solution as a bath. Let the reagent remain on the
metal for 24 hours. Some workers have found that 20 gms. Ammonium
persulphate made up to 100cc., with water gives the best result for brass
and copper.
3. Stainless Steel :- Dilute H2SO4 or 10% solution of HCl in alcohol.
4. Lead (Motor car batteries ,etc.) :-
Glacial acetic acid (3 parts)and Hydrogen peroxide.
This solution has yielded excellent results. Time 10-30 minutes. When the
erased number appears, clean the metal in concentrated nitric acid.
18. 5. Zinc Alloys :-
NAOH 10% solution in water OR
Chromic acid(20gms),NA2SO4 (1.5gms),Water (or) Nitric acid(25%).
Development is slow. So, use the plasticine bath method. Time 10-16 hours.
6. Cast Iron and Cast Steel :-
10% solution of sulphuric acid plus potassium dichromate.
7. Aluminium Alloys (Engine surface of the motor bikes, auto-rickshaw
engine, vehicle identification plates etc.) :-
Villela’s solution - Glycerine, HF(20 ml), Nitric acid (10ml) OR
19. Hume Rothery solution - Copper chloride(200g), HCl(5ml) and water OR
Ferric Chloride (as recommended by FBI Laboratory).
8. Tin surface :- Hydrochloric acid 10 per cent solution. Alternate
swabbing and washing. c. Time 10-20 minutes.
9. Silver :- Concentrated nitric acid. Immerse the specimen for few
seconds. c. After each dipping wash with running water.
10. Gold and Platinum :- Nitric acid 1pt, Hydrochloric acid 5pts, Distilled
water 6 pts.Carry out etching at 15oC. Time 1 hour or longer.
11. Wood :- Play a jet of steam onto the erased surface.The steam softens
the wood and causes the fibres which were bent during punching the
number to spring back and the broken fibres to swell.Where the mark
has been, the wood now projects above the surface and the mark can
be deciphered.
20. 12. Leather :- Clean the surface with cotton-wool swab soaked in
chloroform, and examine under ultraviolet light.Swab the surface
with cotton wool soaked in 2N caustic soda solutions.
13. Rubber :- Some rubber articles are stamped, and when stamping is
erased the suspect area can be treated by lightly swabbing with
petrol or even on occasions carbon- disulphide.This latter solution
acts upon rubber very rapidly and should be used with caution.
