TOOL MARKS

TOOL MARKS

1. TOOL MARKS SUBMITTED TO :- Ms. ARCHANA PATHAK MAM BY :- ASHLESHA S RATNAPARKHI MSc FORENSIC SCIENNCE 1 st 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,   Compression marks / Impressed marks :- These are produced when a tool strikes the surface with pressure. Striated marks :- These are produced when a tool scrapes the surface. Combination of Compression and Striated marks :- These marks as the name suggests are the combination of compression and striated marks. Repetitive marks/ Multistroke marks :- These are produced when a tool strikes the surface a number of times.    

4. 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.

5.   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.  

6. 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 , (CaSO 4 ) 2  1/2 H 2 O is used.

7. 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 ( 71 o C ), 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.  

8. 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 .

9. 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.

10. Types of marks found on the vehicle parts and other articles :-   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.

11. 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

12.   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.            

13. 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  

14. Techniques of restoration The technique of applying the reagent is the same for almost all metals. 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. The reagent is then applied to this surface with a cotton ball, attached to a stick or glass rod. 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.

15.   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.    

16. 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.

17. 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. 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                   

18. 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. Silver :- Concentrated nitric acid. Immerse the specimen for few seconds. c. After each dipping wash with running water. 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.                                                  

19. 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. 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.

20. THANK YOU !

21. REFERENCES https://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/toolmarks Laboratory Procedure Manual – Forensic Physics