Serial Number Restoration. © Precision Forensic Testing Serial Number Restoration – The practice of restoring an obliterated serial number by using scientific.

Serial Number Serial Number RestorationRestoration

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Serial Number Restoration – The practice of Serial Number Restoration – The practice of restoring an obliterated serial number by restoring an obliterated serial number by using scientific methodsusing scientific methods

Serial Number – A unique number typically Serial Number – A unique number typically applied to an object by a manufacturer applied to an object by a manufacturer

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Commonly Marked ItemsCommonly Marked Items Many items have serial numbers placed on Many items have serial numbers placed on

them by the manufacturer. Stereos, them by the manufacturer. Stereos, computers, vehicles, televisions, and almost computers, vehicles, televisions, and almost all electronic equipment have serial all electronic equipment have serial numbers. numbers.

The discussion of this lecture will focus on The discussion of this lecture will focus on firearms and serial numbers applied to firearms and serial numbers applied to them. them.

Firearms are the most commonly Firearms are the most commonly encountered item in crime laboratories with encountered item in crime laboratories with obliterated serial numbers.obliterated serial numbers.

The firearms are made from a variety of The firearms are made from a variety of materials including aluminum alloy, materials including aluminum alloy, stainless steel, and steel.stainless steel, and steel.

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Types of Serial Numbering Types of Serial Numbering Application MethodsApplication Methods

Serial numbers can be applied in a variety of Serial numbers can be applied in a variety of methods. Each method has unique characteristics methods. Each method has unique characteristics which enable them to be differentiated from each which enable them to be differentiated from each other.other.

The method employed by a manufacturer is The method employed by a manufacturer is generally dictated by what is most economically generally dictated by what is most economically efficient. If the manufacturer is already set up to do efficient. If the manufacturer is already set up to do stampings, the serial number may be stamped. If stampings, the serial number may be stamped. If the manufacturer uses laser etching to mark other the manufacturer uses laser etching to mark other parts of the firearm, they may use lasers to etch the parts of the firearm, they may use lasers to etch the serial number. serial number.

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Dot MatrixDot Matrix

Dot matrix Dot matrix engraved serial engraved serial numbers are fairly numbers are fairly shallow and are shallow and are made by a made by a succession of dots succession of dots

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Dot Matrix - ExamplesDot Matrix - Examples

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Dot Matrix - ExamplesDot Matrix - Examples

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Laser EngravingLaser Engraving Serial numbers engraved Serial numbers engraved

with a laser are shallow with a laser are shallow and have a “burned” and have a “burned” appearance. appearance.

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Laser EngravingLaser Engraving

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Laser Laser EngravingEngraving

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Stamped Serial NumbersStamped Serial Numbers

Stamped serial Stamped serial numbers are made numbers are made by using a stamp by using a stamp with a positive with a positive impression of a impression of a number and applying number and applying sufficient pressure to sufficient pressure to impart a negative impart a negative impression of the impression of the stamp on the objectstamp on the object

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Stamped Serial Numbers - TheoryStamped Serial Numbers - Theory

When a serial When a serial number is stamped number is stamped in metal, plastic in metal, plastic deformation of that deformation of that metal occursmetal occurs

After the force After the force causing the causing the deformation is deformation is removed, the removed, the impression remainsimpression remains

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Stamped Serial NumbersStamped Serial Numbers

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Stamped Serial NumbersStamped Serial Numbers

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Stamped Serial Numbers - TheoryStamped Serial Numbers - Theory The compressed area at the The compressed area at the

base of the stamping is base of the stamping is strained below the surface strained below the surface of the stamp markof the stamp mark

The depth of the strained The depth of the strained area is dependant on the area is dependant on the type of metal. For example, type of metal. For example, the strained area of steel the strained area of steel may be affected for may be affected for approximately 6 times the approximately 6 times the depth of the stampdepth of the stamp

The purpose of stamping The purpose of stamping the metal is to impart a the metal is to impart a permanent number used for permanent number used for identifying that itemidentifying that item

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Stamped Serial Numbers - TheoryStamped Serial Numbers - Theory

Stamping a serial Stamping a serial number while the metal number while the metal is below it’s is below it’s recrystallization recrystallization temperature is known temperature is known as “Cold Working”.as “Cold Working”.

When metal is cold When metal is cold worked, the areas that worked, the areas that are worked will change are worked will change properties. These properties. These changes include: changes include: increasedincreased hardness hardness and tensile strength. and tensile strength. However, there are However, there are decreasesdecreases in it’s in it’s malleability and malleability and ductilityductility

Additionally, the Additionally, the position of the metal position of the metal in the electromotive in the electromotive series is raised which series is raised which lowers it’s resistance lowers it’s resistance to oxidationto oxidation

The lowered The lowered resistance to chemical resistance to chemical oxidation allows for oxidation allows for the use of acid to etch the use of acid to etch more efficiently in the more efficiently in the area where the serial area where the serial number was stamped.number was stamped.

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ObliterationObliteration When serial numbers are When serial numbers are

obliterated, they are obliterated, they are generally ground down generally ground down beyond the lowest point beyond the lowest point of the original stamping.of the original stamping.

This results in the visible This results in the visible portion of the serial portion of the serial number being removed.number being removed.

By removing the serial By removing the serial number, criminals hope number, criminals hope that the object can not be that the object can not be identified as having been identified as having been stolen.stolen.

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ObliterationObliteration The serial number is no The serial number is no

longer visible due to the longer visible due to the removal of the top layer removal of the top layer of the metal.of the metal.

The area below the The area below the obliterated layer is obliterated layer is affected by the affected by the stamping process and is stamping process and is the reason serial the reason serial number restoration is number restoration is possible.possible.

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Serial Number Restoration - Serial Number Restoration - ChemistryChemistry

Steel is comprised of iron and carbon. Additional elements Steel is comprised of iron and carbon. Additional elements such as nickel, manganese, chromium, cobalt, vanadium, such as nickel, manganese, chromium, cobalt, vanadium, and molybdenum are added to enhance it’s properties. and molybdenum are added to enhance it’s properties. Sulfur and phosphorus are typically present as impurities.Sulfur and phosphorus are typically present as impurities.

The elements are bound at the atomic levelThe elements are bound at the atomic level Copper salts (Copper Chloride) are common in many metal Copper salts (Copper Chloride) are common in many metal

etching reagents for the purpose of assisting in the etching reagents for the purpose of assisting in the oxidation of ironoxidation of iron

Anodic Reaction: FeAnodic Reaction: Fe00 Fe Fe 2+2+ + 2e-+ 2e-

Cathodic Reaction: Cu Cathodic Reaction: Cu 2+2+ Cu Cu00 + 2e- + 2e-

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Visualizing RestorationsVisualizing Restorations

The reason serial numbers appear when they are The reason serial numbers appear when they are acid etched is due to acid etched is due to specular reflectionspecular reflection..

Specular reflection – light reflecting off a smooth Specular reflection – light reflecting off a smooth surfacesurface

Diffuse reflection – light reflection off rough surfacesDiffuse reflection – light reflection off rough surfaces

Specular Specular ReflectionReflection

Diffuse Diffuse reflectionreflectionSmooth Smooth

SurfaceSurface

Rough Rough SurfaceSurface

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Serial Number Formula ListSerial Number Formula List

Ferric ChlorideFerric Chloride 25 grams Ferric Chloride 25 grams Ferric Chloride

(FeCl(FeCl33)) 100 mL Water (H100 mL Water (H22O)O)

Acidic Ferric ChlorideAcidic Ferric Chloride 25 grams Ferric Chloride 25 grams Ferric Chloride

(FeCl(FeCl33)) 25 mL Hydrochloric Acid 25 mL Hydrochloric Acid

(HCl)(HCl) 100 mL Water (H100 mL Water (H22O)O)

25% Nitric Acid25% Nitric Acid 75 mL 75 mL Water (HWater (H22O)O) 25 mL conc. Nitric Acid (HNO25 mL conc. Nitric Acid (HNO33) )

Fry’s ReagentFry’s Reagent

90 grams Cupric Chloride (CuCl90 grams Cupric Chloride (CuCl22) ) 120 ml Hydrochloric Acid (HCl)120 ml Hydrochloric Acid (HCl) 100 mL Water (H100 mL Water (H22O)O)

Turner’s ReagentTurner’s Reagent 2.5 grams Cupric Chloride 2.5 grams Cupric Chloride

(CuCl(CuCl22) ) 40 mL Hydrochloric Acid (HCl)40 mL Hydrochloric Acid (HCl) 25 mL Ethyl Alcohol (CH25 mL Ethyl Alcohol (CH3 3 CHCH22OH)OH) 30 mL Water (H30 mL Water (H22O)O)

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Serial Number RestorationSerial Number Restoration

An obliterated serial number typically has An obliterated serial number typically has a surface that has been scratched so that a surface that has been scratched so that the number is no longer recognizablethe number is no longer recognizable

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Serial Number RestorationSerial Number Restoration The first step in the process of restoring the serial The first step in the process of restoring the serial

number is to polish the surface by using sand number is to polish the surface by using sand paper in progressively finer grits.paper in progressively finer grits.

Polishing the surface will help in visualizing the Polishing the surface will help in visualizing the serial number.serial number.

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Serial Number RestorationSerial Number Restoration

Acid Etching – The acid reacts with the Acid Etching – The acid reacts with the metal and produces hydrogen gas bubblesmetal and produces hydrogen gas bubbles

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Serial Number RestorationSerial Number Restoration

The result of the acid etching is a restored The result of the acid etching is a restored serial number. The dark appearance of the serial number. The dark appearance of the numbers is the result of diffuse reflection.numbers is the result of diffuse reflection.

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DocumentationDocumentation The final step in performing a serial The final step in performing a serial

number restoration is documenting the number restoration is documenting the recovered serial number. This can be recovered serial number. This can be done by writing down the numbers or done by writing down the numbers or photographing the results. Photographing photographing the results. Photographing serial number restoration may be difficult serial number restoration may be difficult due to the lighting requirements.due to the lighting requirements.

Additionally, the chemicals used to etch Additionally, the chemicals used to etch the metal should be documented in the the metal should be documented in the notes. notes.

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Case StudiesCase Studies

An ATV was suspected An ATV was suspected of having been stolen of having been stolen from a local dealership.from a local dealership.

When police attempted When police attempted to read the VIN (Vehicle to read the VIN (Vehicle Identification Number) Identification Number) it was observed that it it was observed that it had been obliterated.had been obliterated.

The number in question The number in question was located on the was located on the engine engine

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Case StudiesCase Studies

The surface with The surface with the obliterated the obliterated number was number was located on the located on the top of the engine top of the engine blockblock

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Case StudiesCase Studies

This is the area This is the area on top of the on top of the engine where engine where the VIN number the VIN number was stamped. was stamped.

The first step in The first step in the restoration the restoration process will be process will be to sand it to sand it smooth. smooth.

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Case StudiesCase Studies

After the surface After the surface was sanded, Acidic was sanded, Acidic Ferric Chloride was Ferric Chloride was applied to the applied to the engine block.engine block.

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Case StudiesCase Studies The Vehicle Identification Number was The Vehicle Identification Number was

restored to H310E-06674. Using this restored to H310E-06674. Using this information, police were able to verify the ATV information, police were able to verify the ATV was stolen and press charges against the was stolen and press charges against the suspect.suspect.

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Case StudiesCase Studies A shotgun was discovered under a couch A shotgun was discovered under a couch

during a drug raid. While attempting to during a drug raid. While attempting to locate a serial number, it was found to locate a serial number, it was found to have been ground off.have been ground off.

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Case StudiesCase Studies The serial number on the shotgun has The serial number on the shotgun has

been totally ground off.been totally ground off. Once again, the area is sanded smooth to Once again, the area is sanded smooth to

give the best possible resultsgive the best possible results

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Case StudiesCase Studies

25% Nitric acid 25% Nitric acid was applied to was applied to the area that had the area that had been polished.been polished.

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Case StudiesCase Studies

A photograph of A photograph of the serial number the serial number was enhanced to was enhanced to show the number.show the number.

Documenting the Documenting the restored serial restored serial number is number is important when important when the case goes to the case goes to trial and it can be trial and it can be shown to a jury.shown to a jury.

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