Watermark examination is the process by which a Forensic Document Examiner (FDE) tests a watermark to see how well it aids the questioned document analysis, particularly the paper examination report.
There are various types of watermarks on paper, and an FDE should be know how to identify them based on their distinguishing characteristics.
Read this comprehensive guide to learn about those characteristic differences. Plus, what are the different types of destructive and non-destructive tests for forensic watermark examination?
Importance of Watermarks Examination in Questioned Document
With the examination of the watermark on a papered document, the examiner can extract the following information:
- Production House: Paper production company
- Authenticity: Bond paper, security paper, property paper, education certificates, etc.
- Specific Retailer: Many paper companies manufacture paper with custom logos or text as watermarks for their retailer and business partners (or as per their requirements).
- Paper dating: If the logo is changed, it can help in finding an absolute age. Watermark with date/year can easily help to find the age of the papered document.
- Coded Watermarks: Another means of identifying absolute age. Coded watermarks, which not only help to identify the manufacture, but also allow the examiner to possibly determine the year/period the paper was manufactured.
- Location: Multinational/International paper manufacturers majorly tweaks their logo to symbolize their country of origin.
- Quality of sheets: Some companies use translucent marks to define their premium product with normal ones.
- Watermark in Digital Docs: States the trial version of the software, person or company name, digital signature, etc.
Forensic Examination of Genuine Watermarks on Questioned Documents
Before diving into the watermark examination process, the International Organization for Standardization (ISO) recommends the following conditions that should be followed by a Forensic Examination Unit (FDU) while testing the paper.
Testing environment should have:
- Relative humidity: 50 ± 2%
- Temperature: 23 ± 1°C.
1. Physical and Optical Examinations of Watermarks
Physical analysis starts with a simple method— transmittance. It is a two-step process.
First, the document needs to be viewed through transmitted light, and the following details are noted down.
- Size and dimension: Both paper and watermark size and dimension should be evaluated.
- Position: logo placement with paper.
- Alignment: text and logo alignment within the watermark.
- Possible Watermarks type: Artificial (one side translucent), and digital marks can easily be differentiated. True and chemical marks are indistinguishable from human eyes.
- Nature of text: fonts, roundness of edges, relative size.
- Opacity: even opacity, darker and lighter shades in the design.
- Logo detailing: Use of spur, lines, dashes, and other embellishments should be noted.
- Irregularities and defects: Defects, cuts, and marks should be noted.
Quick Note: QDE can use an opacimeter to determine the exact transmittance value for both logo and paper.
For a permanent record of your finding, you should photograph watermarks. These photographs further assist you in a side-by-side comparison of the design.
Quick Fact: Contact prints were used to develop watermarks observation. But they are majorly replaced by high-resolution scanners.
2. Microscopic Examination Using SEM
Topography analysis using Scanning Electron Microscope (SEM) can depict more detailed images of fiber and their arrangement in the paper.
Moreover, details such as ridges, tiny indentations, or depression can be easily evaluated. This makes it easy to differentiate between chemical and traditional watermarks.
Microscopic Differences Between Chemical and True Watermarks
In chemical ones, the watermark fibers appear to be sweller and more disturbed (direction) with a noticeable smoothness than the rest of the paper.
On the other hand, watermarks made during the production process have the same directionality and fiber arrangement throughout the paper, even on the watermark section.
In addition, fibers on true watermarks tend to stretch and align straight perpendicular to the surface. This is due to the fact that as the imprint roller leaves the wet paper, it takes some fiber with it, causing stretching and breaking.
- Paper handling: as little as possible, use gloves or tweakers
- Recommended magnification: 500x to 1200x.
- Detectors: Secondary Electron Detector (SED) and Backscattered Electron Detector (BED)
- Secondary Electron Detector (SED): Gives good depth of field and fineness of paper fibers. Suitable for watermarks made during the production of paper.
- Backscattered Electron Detector (BED): High sensitivity to differences, such as distinguishing between paper fineness due to fibers (which appear darker) and higher elements (lighter). Best for both physical (true) and chemical watermarks.
3. Non-Destructive Spectroscopic Examination
In Spectroscopy analysis, the examination should be done from both sides because chemical watermarks appear better from the side of impregnation.
A. Short Wave UV (180-280nm)
Majorly used for identification of chemical watermarks on bright paper.
Commercially produced stationery papers often have optical brighteners that give a great contrast against these darker-dull patterns of chemical watermarks. This darker shade is because of their absorption of the short UV light.
On the other hand, no distinguished pattern is seen on the true watermark. This is because they are physically altered (stamping on wet) and have all the same chemicals (fillers, OBAs) as the rest of the paper.
Caution: Use protective glass, as short UV is damaging to the human eye.
B. Long Ultraviolet Spectrum (300 to 400 nm)
Matte-finished and non-bright papers with chemical watermarks can be distinguished from traditional watermarks.
Conversely to short UV, here, marks appear to be lighter, whiter, and less opaque than the rest of the paper.
But, the traditional watermarks share shame opacity throughout the paper.
C. Radiography (Soft X-Rays)
As X-ray doesn’t detect organic resins, the exact size watermark can be recorded and compared.
In the Grenz process, paper with a possible chemical watermark is placed between the soft X-ray illumination (rays at 7kV) and X-ray film (source).
This reproduces the exact design on the film without any shades from the rest of the paper.
One advantage of using X-rays is they can be used to study the watermark obstructed by printing or writing over it. Because X-rays don’t absorb carbon-based inks they make them clearly reproducible over X-ray film.
Beta-radiography produces an accurate replication without much interference over a film.
- Time consuming: average 12 hrs.
- Expensive: about $2k for a single plate
- Health hazardous
Quick history: Developed by D. P. Erastov in the late 1950s.
Procedure: The process involves placing the papered watermark in between the beta-isotope plate and X-ray film. Beta-isotope plate irradiated the X-ray though the paper resulted in propositional image reproduction.
E. Raking Reflectance Illumination (RAK)
RAK technology is commonly used for the detection of forged paintings. It gives very clear, contrast strokes of the paintbrush. The same technology can be used for identifying the type of watermarks.
When analyzing the traditional watermarks under RAK, it produces crip and shadowed strokes over the paper. On the other hand, chemical watermarks differ in glossiness due to the application of translucent chemicals.
In examing the sample under blue filter (RAK + Blue Filter), it can distinguish:
- Chemical marks: appear darker and even than rest of paper
- Traditional Watermarks: same shade and uneven surfaces
4. Using Erasures (Destructive Method)
Interesting, destructive, time-consuming, and out-of-date method of defining the type of watermarks.
The principle of this method; chemical paper erasures like Groomstick have cleaning chemicals that may alter the chemical watermarks.
A study published in the Journal of the American Institute for Conservation (JAIC), uses Groomstick (and other erasures) to differentiate between traditional and artificial watermarks.
The procedure of the study was:
- Clean the suspected watermark area with chemical erasures.
- Erase in circular motion (clockwise/anti-clockwise).
- Repeat the motion for at least 25 times.
- Collect crumbs and place them over a watermark, then cover with a polyester film to prevent displacement.
- Sample is placed in a dark, non-humid environment for eight weeks.
- Analyzed the sample under short and long UV illumination.
Observation of study: Darker, dull, opaque fluorescence in short and long wave ultraviolet rays.
Possible Opportunity: You can compare the standard and questioned watermark samples side by side to see how they differ after 24 hours to a week. You can further tweak this eight-week-long test period—that could be an interesting dissertation topic, try yourself.
5. Chemical Analysis of Watermarks (Destructive)
Because of trademark security, companies smartly alter the exact composition of watermarks in their patents. This makes it harder to determine the exact components using chemical analysis.
Plus, they are of destructive nature. Thus, not commonly used by forensic document examiners. But, if needed, they should be analyzed at last.
The most common chemical analysis metric is to study the resins present in watermarks (given by Browning, 1977):
- urea- or melamine-formaldehyde
- Epoxy resins
A. Using Rhodamine Dye
Mixture preparation: Powder mix of 0.25g of rhodamine red dye and 50g of powdered sugar.
- Sprinkle the dry mix of prepared mix.
- Float the paper on water.
- Observe under an ultraviolet lamp.
Indication of forged watermark: Dye will fluoresce as it gets moist if it is an artificial watermark.
B. Test Using Organic Solvents
Translucent chemical watermarks often have organic components and polymers. That makes them readily dissolve in organic solvent and become more opaque.
Here numerous organic solvents are used for the test. The most common ones are:
- Acetic acid
- Carbon tetrachloride
- Select any of the above organic reagents.
- Using a dropper, place a single drop over the watermark
- Let the drop dry.
- Add 2-3 more drops so, it even cover the watermark
- Let them dry thoroughly.
- Repeat the same procedure for a non-watermarked area of sheet.
- Reagent drops make a permanent ring over the paper surface.
- Chemical watermarks fully dissolve, which seems like no watermarks were there.
- In some cases, watermarks slightly shift from their earlier position.
However, all doesn’t dissolve readily. Therefore, other chemical analyses needed to be performed such as the artificial aging method.
6. Artificial Aging Method
Chemical watermarks fade away as the paper ages but under short UV light, they appear crisp and clear.
Using this principle, paper is first artificial aged, so that if it is a chemical watermark, it fades away. And observing under shortwave UV makes them reappear over the paper.
- One questioned watermark sample is placed in an RH controlled aging chamber (check one on Thomascientific.com).
- Temperature is set to 88°C (± 0.5°C)
- RH should be 55% to 60%.
- Maintained for six days.
- Sample is placed in a dry oven without any humidity (check on dry oven on thermalproductsolutions.com).
- Temperature maintained at 100°C.
- Six days run.
- Paper become brown
- Watermarks become opaque and less translucent.
- Clearly visible under short UV illumination.
Testing using chemical erasures, chemical testing using rhodamine and organic solvents, and artificial aging methods in a controlled environment is the destructive examination for watermarks on paper. Thus, FDE should first perform a non-destructive analysis on questioned documents.
Basic optical examination using opacimeter; spectroscopic analysis including short and long UV, soft X-ray; and microscopic analysis using SEM are non-destructive ways to study and identify the types of watermarks.
- Method for applying chemical watermarks on substrate [GooglePatents]
- Detecting Watermarks [Link]
- An improvement in Grenz radiography of paper to record watermarks, chain and laid lines [source]
- Everything you Wanted to Know About Watermarking: From Paper Marks to Hardware Protection [link]
- Forensic Document Examination: Principles And Practice [Book]
- Scientific Examination Of Documents Methods And Techniques [Book]
- Observations on paper as evidence [book]