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Print Process ID
The image is a muted version of what a document examiner might see through a microscope during the examination of a document printed with "Letterpress." To be able to identify printing processes, the examiner must first learn:
1. some basic theory about "non-impact" printing processes
2. how the various printing processes are accomplished
3. what are the important parts of the various printing presses
4. what type of media, or "substrate" are compatible with the process
5. what type of "ink" is compatible with the process
6. how these factors work together to create a printed document
7. what characteristics would be seen under magnification as signs of each printing process.
Following through with our example, in Letterpress, the printing "plate" has two areas, and one is raised above the other. The area that is raised contains the information that is to be printed. When colorant ("ink") is spread onto the plate, it must be kept in the raised area only, or there will be printing where there should be none. The inked plate passes through a printing "nip" where presure forces it against the substrate (often, but not always, this is paper). Due to the nature of the materials and process involved, the pressure forces some of the colorant to the outside of each "cell" of the plate, resulting in a "squeeze-out" effect in which the center of the printed cell has less density of colorant, and the perimeter has a greater density of colorant. When the examiner looks through the microscope, the image may look like a brighter, crisper version of this background.
While this example is somewhat simplified, in general this is how print process identification is done. The examiner understands the process and materials and knows what the results of the process should look like under magnification. The examiner also works with reference books that diagram and explain the printing processes and keeps a library of images as benchmarks of the various printing processes.
An excellent seminar in Print Process Identification for Forensic Document Examiners is offered at Rochester Institute of Technology. The image for this page were captured by one of the seminar instructors, RIT professor Milton Pearson, and is used here with his permission. Thanks, Milt!
1. some basic theory about "non-impact" printing processes
2. how the various printing processes are accomplished
3. what are the important parts of the various printing presses
4. what type of media, or "substrate" are compatible with the process
5. what type of "ink" is compatible with the process
6. how these factors work together to create a printed document
7. what characteristics would be seen under magnification as signs of each printing process.
Following through with our example, in Letterpress, the printing "plate" has two areas, and one is raised above the other. The area that is raised contains the information that is to be printed. When colorant ("ink") is spread onto the plate, it must be kept in the raised area only, or there will be printing where there should be none. The inked plate passes through a printing "nip" where presure forces it against the substrate (often, but not always, this is paper). Due to the nature of the materials and process involved, the pressure forces some of the colorant to the outside of each "cell" of the plate, resulting in a "squeeze-out" effect in which the center of the printed cell has less density of colorant, and the perimeter has a greater density of colorant. When the examiner looks through the microscope, the image may look like a brighter, crisper version of this background.
While this example is somewhat simplified, in general this is how print process identification is done. The examiner understands the process and materials and knows what the results of the process should look like under magnification. The examiner also works with reference books that diagram and explain the printing processes and keeps a library of images as benchmarks of the various printing processes.
An excellent seminar in Print Process Identification for Forensic Document Examiners is offered at Rochester Institute of Technology. The image for this page were captured by one of the seminar instructors, RIT professor Milton Pearson, and is used here with his permission. Thanks, Milt!
Faded Writing
We all have to do our taxes, right? And, sometimes we put it off till almost the last minute, right? Have you ever been sorting through your financial documents and come upon a cash receipt that is so badly faded that you can barely read any of the information? No idea who was the vendor or what was the amount? Maybe it is even a blank paper, but just the right size and paper type to be some sort of receipt.... You need to account for all that cash you spent, and this receipt could be important. Well, you are not alone. It probably happens to everyone. It happened here this week.
This totally "blank" slip of paper was in the pile of receipts being recorded. In other circumstances, it would probably have been thrown away as a useless scrap of paper. But, at tax time, and in the tax receipt folder, this must have had some meaning.
Ink that fades to invisibility can leave behind traces that can be seen only when reactions to Ultraviolet (UV) and Infrared (IR) radiation are considered. The "blank" receipt was placed in the VSC-4 (Video Spectral Comparator).
Green light (wavelength 480-620 nm, or nanometers) was directed at the document. An IR filter (645 nm) was inserted in front of the video camera of the unit. The result, shown here, was that the invisible, but remaining, traces of ink luminesced (glowed). This luminescence could not be seen with the naked eye because it was at a wavelength outside that of visible light.
The VSC camera is sensitive to IR radiation. The IR filter blocked out all visible light so that only radiation longer than 645 nanometers could be seen by the camera. The monitor of the VSC shows the examiner what the camera sees - glowing letters instead of a blank slip of paper. A print was made on the attached printer to satisfy the IRS, and a frame grabber was used to capture the image for display here.
So who says tax time isn't fun? Any time a blank slip of paper suddenly glows with information is a good time if you are a document examiner. Keep this in mind if you ever need to restore faded writing, uncover an obliteration, recapture erased information, see differences in ink on a document, or look at a document in a new way.
If you would like to see more lab equipment at work, take a tour of the newly-expanded, QDEWill forensic document examination laboratory.
We all have to do our taxes, right? And, sometimes we put it off till almost the last minute, right? Have you ever been sorting through your financial documents and come upon a cash receipt that is so badly faded that you can barely read any of the information? No idea who was the vendor or what was the amount? Maybe it is even a blank paper, but just the right size and paper type to be some sort of receipt.... You need to account for all that cash you spent, and this receipt could be important. Well, you are not alone. It probably happens to everyone. It happened here this week.
Ink that fades to invisibility can leave behind traces that can be seen only when reactions to Ultraviolet (UV) and Infrared (IR) radiation are considered. The "blank" receipt was placed in the VSC-4 (Video Spectral Comparator).
Green light (wavelength 480-620 nm, or nanometers) was directed at the document. An IR filter (645 nm) was inserted in front of the video camera of the unit. The result, shown here, was that the invisible, but remaining, traces of ink luminesced (glowed). This luminescence could not be seen with the naked eye because it was at a wavelength outside that of visible light.
The VSC camera is sensitive to IR radiation. The IR filter blocked out all visible light so that only radiation longer than 645 nanometers could be seen by the camera. The monitor of the VSC shows the examiner what the camera sees - glowing letters instead of a blank slip of paper. A print was made on the attached printer to satisfy the IRS, and a frame grabber was used to capture the image for display here.
So who says tax time isn't fun? Any time a blank slip of paper suddenly glows with information is a good time if you are a document examiner. Keep this in mind if you ever need to restore faded writing, uncover an obliteration, recapture erased information, see differences in ink on a document, or look at a document in a new way.
If you would like to see more lab equipment at work, take a tour of the newly-expanded, QDEWill forensic document examination laboratory.