1. Restoration of Obliterated Marks ,Tool marks, Mechanical Fit & trace analysis
The Electronic equipment's ,Automobiles &Fire arm are provided with serial numbers as a means of Identification or to establish ownership.
Owners inscribe their names on valuable utensils & wares for identification.
When such articles are stolen or involved in crime serial numbers & markings are destroyed by criminals by filing or grinding them.
Obliterated marks can be restored ‘
These markings can be restored on material other then metal such as wood, plastics &fiber glass’
Different Metals &alloys require specific method for restoration by Forensic Experts.

2. Type of Marks.
Three types of Marks are commonly found on the Articles.
Cast Marks-These marks are raised above the surface of the Metal.
Such marks form part of the Mould &appear on the metal surface when it is cast .
If these marks are erased it is not possible to restore them.

3. Punched Marks.
The marks on article are made by striking hard steel dies.
Which result in the compression of the metal &disturbance on the surface underlying it.
Restoration is possible if has been not deeply erased/grinded.

4. Engraved Marks.
They are made by using electric engraver or pointed Chisel.
Less pressure is applied leaving very little alteration of crystal structure of the metal.
The marks can be restored provided the erasure is not deep.

5. Restoration Of Obliterated Marks
When serial number is stamped into piece of Metal .
The Metal structure beneath the stamped letter & digits is disordered.
Traces of disordered structure often remain after the serial number has been filed or grinded.
The criminal removes the stamped marking by grinding &filing till it is not visible.
The marks are strained & extend s a short distance beneath the indented number or marks.
When a suitable chemical reagent is applied.

6. The strained &unstrained areas will dissolve the metal at different rates.
This unequal dissolution rate helps in bringing out the original number or Marks.
If Marks or number are erased deep &reach the inner thickness it is usually not possible to restore the number or marking.
Occasionally a tool marks are in the form of scrape an examiner can see pattern of irregular ridges & valley through a microscope.
It may be possible to match the pattern with those on a suspected tool used in the crime.

7. Tool Marks. These are marks ,impressions or cut left on a by a Tool.
These are generally found in cases of burglary where there is forcible entry.
That is dented wood or marks on wooden door or window frame if opened with Screwdriver or Crowbar.
In this cases Photographs of these marks be taken.
Make cast of marks by P.o.P or by dental cement.
So that it can be used for comparison with evidence that is recovered later.

8. Type Of Marks.
Compression Tool Marks-Marks formed when a tool is pressed into a softer material &such marks often show the outline of the working surface of tool as such class characteristics of the tool (dimension) can be determined.
Individual characteristics of tool may be more difficult ‘

9. Sliding Tool Marks.
Marks formed when a tool slides along the surface & consist of parallel striations.
Class characteristics are more difficult to determine.
That is Screwdriver chisel &pry base could make similar sliding marks.

10. Cutting Tool Marks.
Marks are combination of compression & sliding tool marks ‘
The cutting tool indents material being cut & as it does so the working surface of tool slides over the cut surface.

11. Principle Of comparison of Tool marks
It is impossible to manufacture two tools which are exactly alike.
Most of the tools used in crime are not manufactured under controlled condition.
Therefore show gross differences in addition to microscopic variations.
Their regular repeated use result in wear, dents etc.
Reshaping of tools will introduce additional features or alter original features which make tool distinguishable from one another.

12. Examination ,Preservation &Collection
Tool marks may be located on doors ,windows ,locks , cabinet , Almirah ,& safe etc. .
Marks of jack ,or tool used for bending iron bars of window, axe marks on trees or wooden plank ,cut ends of copper &other wires may be located in crime scene involving these objects.

13. Preservation Of Tool Marks.
Take close up Photograph showing location of tool marks.
If possible the object having tool marks may be transported to laboratory.
Make cast marks of tool marks using dental cement or silicon rubber.
Tool left at the spot be wrapped with cotton on the working edge.

14. Preparation of test marks.
If it is not possible to send tool to the laboratory make several impressions on similar material as that of the evidence .
Using successive parts from the entire marking area of the tool.
The control should be protected covering with soft cotton or tissue paper & similar packet should be made of the object bearing the crime tool marks& enclosed in a box.

15. Mechanical Fit.
The most conclusive evidence of commonality of a source in any evidence material is a Physical match.
It is an exact fit of broken edges of two pieces of evidence.
If the broken edges of ntwo pieces of a glass can be fitted together exactly mechanical fit condition has been achieved.

16. Examples of Mechanical Fit.
In cases where any broken piece of tool or implement used by the suspect is found at the spot &other recovered from suspect.
Hit &Run accident cases broken head lamps glass, wind screen& chips of paint found at the spot can be mechanically fit on suspected vehicle.
Similarly broken pieces of wooden parts of tool from the spot may be placed together with recovered tool.
Sometimes extension marks present on cut edge on wire insulation can be made to fit the other piece of wire evidence to prove that both piece of wire once single piece.
Broken pieces are also found at the crime scene apiece of Knife may be discovered at the scene of assault or Murder or in the wound of victim if other part of the knife can be recovered the two parts can be physically fitted together.