SUBJECT FORENSIC SCIENCE
Paper No. and Title PAPER No. 8: Questioned Document
Module No. and Title MODULE No.21: Rubber Stamp and Seals
Module Tag FSC_P8_M21
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
TABLE OF CONTENTS
1. Learning Outcomes
2. Introduction
3. Stamp and Seal Impression
4. Characteristics of Rubber Stamp and Seal Impression
5. The Examination Process
6. Summary
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
1. Learning Outcomes
After studying this module, you shall be able to: Know about the Rubber stamps and Seal Impression. Identify the Characteristics of Rubber Stamps and Seal Impression. Learn about the Examination procedure for analysis of Rubber and Seal impression.
2. Introduction
Rubber Stamp 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. Increasingly the vulcanized rubber image with an adhesive foam backing is attached to a cling vinyl sheet which allows it to be used with an acrylic handle for support. These cling rubber stamps can be stored in a smaller amount of space and typically cost less than the wood mounted versions. They can also be positioned with a greater amount of accuracy due to the stamper's ability to see through the handle being used. Temporary stamps with simple designs can be carved from a potato. The ink coated rubber stamp is pressed onto any type of medium such that the colored image is transferred to the medium. The medium is generally some type of fabric or paper. Other media used are wood, metal, glass, plastic, rock. High volume batik uses liquid wax instead of ink on a metal stamp.
Seal A seal is a device for making an impression in wax, clay, paper, or some other medium, including an embossment on paper, and is also the impression thus made. 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.
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.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
In most traditional forms of dry seal the design on the seal matrix is in intaglio (cut below the flat surface) and therefore the design on the impressions made is in relief (raised above the surface). The design on the impression will reverse (be a mirror-image of) that of the matrix, which is especially important when script is included in the design, as it very often is. This will not be the case if paper is embossed from behind, where the matrix and impression read the same way, and both matrix and impression are in relief. However engraved gems were often carved in relief, called cameo in this context, giving a "counter-relief" or intaglio impression when used as seals. The process is essentially that of a mould. Most seals have always given a single impression on an essentially flat surface, but in medieval Europe two-sided seals with two matrices were often used by institutions or rulers (such as towns, bishops and kings) to make two-sided or fully three-dimensional impressions in wax, with a "tag", a piece of ribbon or strip of parchment, running through them. These "pendent" seal impressions dangled below the documents they authenticated, to which the attachment tag was sewn or otherwise attached (single-sided seals were treated in the same way).
In the 1982 edition of Scientific Examination of Questioned Documents, Ordway Hilton wrote: “As an office laborsaving device, the hand or impression stamp is convenient to use and useful; as a field of investigation for the document examiner, it is rather infrequent but diversified. Much of its diversity lies in the great variety of stamps in use: those of fixed letter design, those made up entirely of loose type, the facsimile signature stamp, those with rotating sections of the time-date stamp variety, the date stamps with movable strips of type, and any combination of these. The diversity is not limited to classifications based upon makeup. The actual material from which the stamp is constructed and its mode of manufacture adds to the possible varieties.”
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
3. Stamp and Seal Impression
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 forensic document examiners in their casework: the hand stamp, the self- inking stamp, the pre-inked stamp, and the flat-die stamp. Personal, business, and industrial use rubber stamps are produced by the same manufacturing processes and are classified by the ink source. However, the die materials and inks differ in the industrial setting due to the marking needs of a particular industry. Even though discussion in this text is limited to personal or business use rubber stamps, the forensic document examiner should be aware that other die materials are used in the industrial setting. Personal and business use hand and self- inking stamps contain dies made of vulcanized rubber or photopolymer. The die of a hand stamp is mounted on a die plate attached to a knob handle mount or a molded mount. Because the die is exposed to its surrounding environment, it is subject to damage and debris contamination. Inking of the die is accomplished by manually pressing the die onto the stamp pad in order to obtain ink coverage. The inking process of the hand stamp is achieved manually, while the inking process of the self-inker is achieved mechanically. The self-inking stamp consists of a container (usually plastic) that houses the stamp die and ink pad. Since the die is in a container that usually has a cover, it is protected from excessive debris contamination or cuts and other damage that can occur as a result of colliding with other objects one may find in or on a person’s desk. For inking, the die rotates 180° to press into the ink pad when the top of the container is pressed down. The first two classifications concern dies that primarily use water-based inks. The third classification includes pre-inked stamps characterized by a high relief die and, as a general rule, use oil-based inks. 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, and it has a low- or no- relief die, with the ink pad sandwiched between the die and the die holder. Depending upon their intended use, water- or oil-based inks are used in flat-die stamps.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
4. 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., failing to hold the stamp correctly, creating an uneven impression, and using too much force when making the impression, causing the stamp to bounce. Differences are observed between impressions made by hand or self-inking stamps and pre- inked stamps. As a general rule, it would be difficult to make a definitive statement as to the type of stamp that made the questioned impression. However, characteristics observed in a stamp impression can provide clues as to the die material of the suspected stamp. 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. Whether the material is vulcanized rubber or photopolymer, they share the same characteristics in their impressions, as follows:
o Even Ink Coverage o 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. o Absence of an indentation in the ink line. o Rounded beginning and ending of letters. o If water-based ink is used, the bleeding of ink through the paper is minimal. o Ink filling in sharp angles and intersection points of two lines. o Some patchy areas within the inked impression may be observed. o Uneven outline of the letter.
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.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
Since the die of a pre-inked stamp is soft and has some flexibility, the impression differs slightly from the characteristics one would observe in an impression produced by a hand or self-inking stamp. The characteristics observed may include: o Clean and concise detail o Even ink saturation throughout the individual characters o Absence of a heavier ink line on the inside or outside of the letterform o Feathering or bleeding of ink on the edges of the letter o Rounded beginnings and endings of letters o Absence of an indentation in the ink line o Blurring or distortion in small typed text o Oil-based ink bleeding through the paper
Flat-die stamps are divided into two categories: light-burst and thermal printer technology. Light-burst technology uses a Xenon flash to seal the non-print area of the die. The only pores left open that allow ink to pass through the die will be the printed areas. Heat is used in the thermal printer technology to seal the micropores in the non-print area of the flat die. The characteristics of an impression from either flat-die category closely mirror the characteristics found in the pre-inked stamp impressions. However, a few of the flat-die stamps produce impressions that contain characteristics that are more unique to a particular model. For example, the Brother SC 300 PC makes flat-die stamps using thermal printer technology. This particular model was one of the first flat-die machines marketed to the general public. The impression made from a Brother SC 300 PC flat-die stamp will reflect a dot matrix pattern within the printed text. The dot matrix pattern varies in relation to the type size of the text. As the type size becomes smaller, the matrix evolves into a saw tooth pattern. Conversely, the larger the stamp, the more dots in the printed text. Aside from the unique pattern, the remaining characteristics of the impression mimic those observed in other pre- inked stamp impressions.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
5. The Examination Process
A great deal of evidential information is overlooked when a stamp impression on a document is not included in the examination. By taking the time to examine the overlooked evidence, the document examiner may be able to provide additional information to the submitter. For example, a case was submitted requesting handwriting, signature, and printing process examinations in a group of documents. The investigator did not ask about the notary stamps. Because the stamp impressions were included in the examination, the submitter was given additional investigative information, as the microscopic examination of the stamp impressions revealed that they were the product of an inkjet printer and not a rubber stamp. 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. The procedure discussed in this section contains more detail than that found in the guide, but is in agreement with the published ASTM guide. The examination of a rubber stamp or an impression requires a methodological approach. As with any document examination, 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. Having a knowledge base of the various die materials and the manufacturing processes employed to produce rubber stamps is key to assigning proper weight to any observed anomalies. There are two main types of defects: those that occur in the manufacturing process and those that occur through use or abuse of the stamp. Sources of manufacturing defects 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.
In order to classify or determine the source of the defect, the document examiner must have the suspected 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. For example, an air bubble can occur in different stages of manufacturing. The air bubble would be a class characteristic if it is in the Bakelite mold used to produce vulcanized rubber stamps. Every stamp made from that particular mold would have the air bubble in the same location.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
If the air bubble was created by air becoming trapped during placement of the rubber on top of the Bakelite mold prior to vulcanization, the air bubble would be unique to that die and, therefore, would be an individual characteristic. Individual defects more commonly occur through use or abuse of the stamp. Dirt, paper, fiber, accumulated ink, nicks and cuts, edge wear and breakdown, and stamp distortion are a few of the causes for defects to appear in the impression.
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, fiber, and accumulated ink are transitory and can be removed as a result of handling or cleaning of the die. Nicks, cuts, edge wear and breakdown, and stamp distortion are permanent defects, as they are a part of the die. Both transitory and permanent objects can create individual defects that can assist in the identification or elimination of a stamp making a suspected impression. 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. If the image was created by another printing process and not by a rubber stamp, the document examiner is limited to a qualified report, as he or she is restricted to examining only the gross characteristics of the text, i.e., the image reflects the same general class characteristics of type style, type size, arrangement, and design of the submitted rubber stamp.
If the suspected stamp is submitted, conduct a visual inspection to determine the presence of permanent or transitory defects. Determination of ink source and the condition of stamp die, container, and ink pad also can be made during this visual inspection. The container or mount (if a hand stamp) contains an index (also known as the title) that frequently is made from one of the first impressions of the stamp. The name of the stamp manufacturer or stamp shop that made the stamp may be displayed on the container and handle. This information may assist in locating the business that made the stamp.
A microscopic examination to search for anomalies follows the visual inspection. Notation of both the visual and microscopic inspections should be made. It is a good practice to photograph the stamp and its die in order to record its condition when it was submitted. Once this step has been completed, the next step is to compare the submitted rubber stamp to the questioned impression. Are they in agreement in class characteristics: type size, type style, arrangement, and design? If so, the examination proceeds forward. If there is any disagreement in class characteristics, an elimination is justified, as the submitted rubber stamp could not have produced the suspected impression.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
The microscopic examination of the stamp die and the impression should include both direct and oblique lighting. 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. 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.
It is important to stress that the stamp die should not be cleaned until numerous impressions have been made that reflect the condition of the stamp when submitted. Ink saturation and the angle at which the stamp die contacts the printing media determine whether defects on the die will be replicated in the impression. A heavily inked impression may not reveal a small defect due to filling of ink of the void area. It is unknown how the stamp was held by the suspect or the angle of the die as it contacted the paper. Because of these unknown factors, the forensic document examiner produces numerous known impressions of varying ink saturations and of the die contacting the paper at differing angles. 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 ink coverage in the impression will be at its optimum in the first impression. By not re-inking between impressions, the ink coverage gradually decreases with each successive impression. From the 10 to 20 consecutive impressions, the document examiner should observe a decrease in the ink saturation with each successive impression.
The classification of the stamp will determine the range of ink saturation that can be obtained from a suspected stamp. For example, impressions made from a hand or self-inking stamp will reflect a wide range of ink saturation compared to impressions made from a stamp die that is not inked in between impressions. A pre-inked stamp, such as a pre-mixed gel, has its ink in the die.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals
The document examiner must produce the consecutive impressions quickly in order to observe some decrease in the ink saturation. The range of ink saturation is not as dramatic in pre-inked stamps because the ink-filled die is comprised of impregnated or microencapsulated inked cells. The consecutive impressions must be made quickly to prevent the cells from replenishing ink to the top portion of the die that contacts the paper. 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.
The next step is to change the angle of the die contacting the paper when making an impression. Obtaining impressions where even pressure is applied to the die allows the examiner to determine how evenly the ink is dispersed throughout the text. Impressions produced by the die contacting the paper unevenly (at differing angles) allow the document examiner to observe how the impression appears when angles and pressure applications change. 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.
6. Summary
1. 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. 2. A seal is a device for making an impression in wax, clay, paper, or some other medium, including an embossment on paper, and is also the impression thus made. 3. Based on the ink source location, there are four main types of conventional stamps encountered by forensic document examiners in their casework: the hand stamp, the self-inking stamp, the pre-inked stamp, and the flat-die stamp. 4. 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. 5. The document examiner must produce the consecutive impressions quickly in order to observe some decrease in the ink saturation.
FORENSIC SCIENCE PAPER No.8: Questioned Document MODULE No. 21: Rubber Stamp & Seals