EXAMINATION OF SEAL IMPRESSIONS

1. Examination of Seal Impressions
By: CHHAVI KAUSHAL
M.Sc Forensic Science & Criminology
4th Semester

2. Contents
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Impressions
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Rubber stamps
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History
●
Seal
●
Stamp Classification
●
Characteristics of Rubber
Stamps and Seal Impressions
●
Self-inking Stamp dies
Characteristics
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Pre-inked Stamp Characteristics
●
Examination
●
Examination of Seal
Impressions
●
Examination on the Basis of
Defects
●
Steps of Examination
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Criteria for Conclusions
●
Case Study
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References

3. Impressions
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Mechanical impressions are impressions placed on a
piece of paper by a machine or simple tool (e.g.,
typewriters, check writers, rubber stamps and seals).
●
It is often possible to identify the impression left on a
document as produced by one particular machine or tool.
●
It is also possible to determine whether two documents
have a common source, typewriter make and model
determinations and identification of photocopy
machines.

4. Rubber Stamps
●
Rubber stamping, also called
stamping, is a craft in which
some type of ink made of
dye or pigment is applied to
an image or pattern that has
been carved, molded, laser
engraved or vulcanized, onto
a sheet of rubber.
●
The rubber is often mounted
onto a more stable object
such as a wood, brick or an
acrylic block.

5. History
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Prior to 1970, the materials used for conventional rubber stamp dies were either
vulcanized rubber for self-inking stamps or pre-mixed gel for pre-inked stamps. The
manufacturing process of vulcanization using the Ludlow or the Linotype was used for
both materials.
●
In the late 1970s liquid photopolymer as a die material was introduced by UV process.
●
Later in 1990s until the introduction of flat-die stamps, the number of pre-inked stamp
manufacturers was small due to the high manufacturing costs associated with this type
of process.
●
The introduction of light-burst and thermal manufacturing processes expanded the pre-
inked stamp market.

6. Seal
●
A seal is a device for making an
impression in wax, clay, paper, or
some other medium, including an
embossment on paper.
●
The original purpose was to
authenticate a document, a
wrapper for one such as a
modern envelope, or the cover of
a container or package holding
valuables or other objects.

7. Continue..
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The seal-making device is also referred to as the seal matrix or die;
the imprint it creates as the seal impression (or, more rarely, the
sealing).
●
If the impression is made purely as a relief resulting from the greater
pressure on the paper where the high parts of the matrix touch, the seal
is known as a dry seal; in other cases ink or another liquid or liquefied
medium is used, in another color than the paper.

8. Stamp Classification
●
Stamp classification is not based on the type of die
material, but rather the location of the ink source.
●
Based on the ink source location, there are four main
types of conventional stamps encountered by FDEs in their
casework:
A The hand stamp,
B The self-inking stamp,
C The pre-inked stamp,
D The flat-die stamp.

9. ●
Based on the ink source and the manufacturing
process:
A Personal, business,
B Industrial use rubber stamps
●
The third classification includes pre-inked stamps
Salt- leached rubber, foam and powder, and premixed
gel are the materials used to make high relief pre-inked
stamps.
●
The flat-die stamp is the fourth classification

11. Characteristics of Rubber Stamps
and Seal Impressions
●
The characteristics a forensic document examiner observes in stamp
impressions are influenced by the die material, whether the ink is water based
or oil based, the size of the stamp, the type of paper, the interaction of the ink
to the paper, and the individual making the impression.
●
The two most common causes of a less-than-perfect stamp impression involve
the mechanics of stamping, i.e.,
A failing to hold the stamp correctly,
B creating an uneven impression,
C Using too much force when making the impression,
D causing the stamp to bounce.
●
Differences are observed between impressions made by hand or self-inking
stamps and pre-inked stamps.

12. ● Vulcanized rubber and photopolymer are the most common materials used for hand and
self-inking stamp dies. These two materials are non-porous and do not retain ink.
These two mostly share same characteristics:
i Even Ink Coverage
ii Ring of darker ink outlining the individual letter. Known as the “squeegee effect,” this
ring occurs as a result of the relief of the printing area squeezing the ink out to the edge
of the ink line. This characteristic is difficult to observe if the entire character is heavily
inked.
iii Absence of an indentation in the ink line.
iv Rounded beginning and ending of letters.
v If water-based ink is used, the bleeding of ink through the paper is minimal.
vi Ink filling in sharp angles and intersection points of two lines.
vii Some patchy areas within the inked impression may be observed.
viii Uneven outline of the letter.
Self-inking Stamp Dies
Characteristics

13. Pre-inked Stamp Characteristics
●
Due to its porosity, the die of a pre-inked stamp serves as its own ink
reservoir. The materials commonly used for pre-inked dies include pre-
mixed gel, salt-leached rubber, and foam and powder.
●
Dies made of foam and powder can contain water- or oil-based ink.
The remaining die materials only use oil-based inks for personal or
business use.
●
These stamps are soft and have flexibility, therefore show different
characteristics.

14. The characteristics observed may include:
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Clean and concise detail
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Even ink saturation throughout the individual characters
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Absence of a heavier ink line on the inside or outside of the letterform
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Feathering or bleeding of ink on the edges of the letter
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Rounded beginnings and endings of letters
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Absence of an indentation in the ink line
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Blurring or distortion in small typed text
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Oil-based ink bleeding through the paper
Continue...

16. Examination
●
An examination of a disputed document is a scientific problem and it is no
longer confined to comparison of signature or writing but it also includes
examination of ink, typed matter, printed matter, watermark and all other
elements that combine together to form a document. The examination of a
document is not complete until its every element has been studied and
examined thoroughly.
●
When conducting examinations, forensic document examiners must have
known specimens to which they compare the material in question. These
samples may come from any number of known sources, such as a
particular ink manufacturer or machine.
●
First is the preliminary examination which includes paper examination,
no. of folds, writing continuty, unnatural spacing, etc. then the specific
examination is done for more details.

17. Examination of Seal Impressions
●
Questioned documents bearing rubber stamp impressions,
embossed seals, watermarks, or other mechanically printed marks
may be submitted for examination. When possible, it is best to
provide the examiner with any suspected devices associated with
the questioned document that may have been involved in its
preparation. This includes writing instrument(s), papers, or other
substrates, rubber stamp(s), sealing devices (such as notary seals),
printing devices or other mechanisms.
●
The Standard Guide for Examination of Rubber Stamps, ASTM E
2289-03, published by the American Society for Testing and
Materials International, is a guideline of procedures forensic
document examiners should follow in their examination of cases
involving rubber stamps and their impressions.

18. Continue...
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The forensic document examiner must consider the
limitations inherent in the evidence.
●
Intrinsic limitations in the rubber stamp impression
are determined by a combination of the following
factors: the manufacturing process, the material
used for the stamp, the type of ink, the type of
material hosting the impression, and the stamping
style of the individual operating the stamp.

19. Examination on the Basis of
Defects
Mainly 2 types of defects are examined:
●
Those that occur in the manufacturing process which include damage to the
original image, defective die material, distortion or misalignment, poor quality
control, damage caused by cutting the stamp, bubbles, and impurities such as dirt.
●
Those that occur through use or abuse of the stamp.
Determination or classification of defects cannot be made from the examination
of the impression. The defect’s significance, i.e., class or individual, is
determined by the stage of occurrence within the manufacturing process.
Individual defects more commonly occur through use or abuse of the stamp.

20. Continue...
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Individual defects can be transitory and care must
be given in the handling of the stamp so as not to
affect the amount or location of the object causing
the defect. For example, dirt, hair, etc.
●
Nicks, cuts, edge wear and breakdown, and stamp
distortion are permanent defects, as they are a part
of the die.
●
Both transitory and permanent defects can assist in
the identification or elimination of a stamp.

21. Steps of Examination
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Photographs of the stamp and its die is taken in
order to record its condition when it was
submitted.
●
The first step in the examination of a stamp
impression is to examine it microscopically to
make sure you have a stamp impression and not
an image created by another printing process,
such as an inkjet printer or a copier.
●
A microscopic examination to search for
anomalies follows the visual inspection.

22. Continue...
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Once this step has been completed, the next step is to compare
the submitted rubber stamp to the questioned impression.
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The microscopic examination of the stamp die and the impression
should include both direct and oblique lighting.
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Direct lighting provides even illumination of the area being
examined to determine the manufacturing process used to create
the die.
●
Oblique lighting coupled with a higher magnification narrows the
focus of the examination to detect even the smallest of defects
and to determine whether they are permanent or transitory.

23. Continue..
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Upon completion of a thorough examination of the stamp die, an
impression-to impression examination is conducted.
●
The forensic document examiner makes numerous impressions from
the submitted stamp on a substrate that is similar to the material
hosting the questioned impression.
●
If the submitted stamp die is covered by transient material (dirt, hair,
accumulated ink, etc.) and the questioned impression does not reflect
defects that may have been sourced to the transient material, it may be
necessary to clean the stamp in order to obtain impressions free from
transient materials.
●
Prior to cleaning, the stamp should be photographed to document the
condition in which it was received.

24. Continue...
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Collecting a series of impressions without re-inking the die
of the suspected stamp is the proper method of obtaining
impressions with a progressive decrease in ink saturation.
●
For a self-inking or hand stamp, make sure the die is
adequately inked prior to producing the first impression.
●
The classification of the stamp will determine the range of
ink saturation that can be obtained from a suspected stamp.
●
The document examiner must produce the consecutive
impressions quickly in order to observe some decrease in the
ink saturation.

25. Continue..
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Even though flat-die stamps are categorized as pre-inked stamps, obtaining
lighter impressions from continuous stamping is difficult. Since ink only exits
through the open pores of the text, the ink supply is not depleted.
●
A characteristic of a flat-die impression is that the ink saturation will be the
same from the 1st through the 20th successive impression.
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The next step is to change the angle of the die contacting the paper when
making an impression.
●
Rocking the stamp side to side or front to back can cause transient
characteristics directly attributable to the improper handling of the stamp
during the production of the impression.
●
Once the known impressions have been produced, a side by- side comparison is
conducted with the questioned impression to determine if they came from the
same source.

26. Criteria for Conclusions
●
Upon completion of the examination, the document
examiner issues a conclusion based on the
evidence.
●
The conclusion criteria regarding a rubber stamp
impression can be found in the Standard Guide for
Examination of Rubber Stamps, ASTM E 2289-03,
published by the American Society for Testing and
Materials International.

27. Case Study
To illustrate the value of a manufacturer’s mark, consider a 1989 case
when a young girl was kidnapped and murdered. Investigators called
in forensic document examiners to examine the plastic garbage bag in
which the victim was found. Minute markings created by the heat-
seal process used in manufacturing such bags enabled investigators to
determine that the bag was manufactured on the same machine within
seconds of other bags found in the parents’ house. This was key
evidence that resulted in the conviction of the girl’s mother for
murder.

28. References
●
World of Forensic Science, ©2006 Gale Cengage
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http://www.forensicsciencesimplified.org/docs/how
.html
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“Question Documents”: Albert S. Osborn
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1516250384FSC_P8_M21_e-text
●
Questioned Document Overview – 2011
●
Jan Seaman Kelly and Brian S. Lindblom -
Scientific Examination of Question

29. Thank you