Origin markings have been applied to firearms for centuries. While the initial focus was on accounting for equipment used in the military, today manufacturers of hunting and sporting firearms in all countries are also required to mark and serialize for traceability purposes. It is noteworthy that the marking requirement in the U.S. has only existed since the 1960s. Serial markings on firearms in accordance with regulations can be viewed in their entirety as visible and tactile, superficially direct markings, and their in-depth "echoes". Depending on the marking method, an embossing depth of up to two millimeters can be achieved. While dot peen marking interfere less with the material, roll marking or punches emboss much deeper. In general, in firearms forensics the task is to restore poorly readable or no longer recognizable manufacturer's markings. This problem may also arise naturally through rust or other corrosion damage, even without further criminal motives. The combination of their removal by grinding, re-bluing or other subsequent surface coatings, such as electroplating or painting, usually unintentionally obliterates original markings as well.
The lasting impression: simple methods of restoring serial numbers on firearms
The targeted grinding out of the serial number serves dark purposes in order to make it more difficult to trace a crime weapon or – for the perpetrator – ideally to prevent it. The forensically active counterpart, however, quickly developed recovery methods. Even the first standard work on modern firearms forensics from 1935, "Firearms Investigation Identification and Evidence" by Major General Julian S. Hatcher, goes into this in detail. The principle of all restoration processes on metallic materials uses the microstructural change during mechanical processing. Markings stamped on metallic surfaces by rolling or punching can certainly be recovered even after grinding them out, analogous to their in-depth structural change. Forensic experts therefore look for the material compressed under the original marking. These compression under the markings, now unrecognizable due to grinding or rust, form the "echo" of the former markings, which is still present in the depth. However, the classical method of this process is done in a surface-destroying way.
First techniques for the restoration of markings were often unsuitable: firearm genuine, but ruined after testing
The area in question is ground down and then polished to a mirror finish. Acid is applied to the surface prepared in this way, which attacks the material selectively, i.e. depending on the microstructure. The polished surface is usually wetted several times with a swab, dried and rubbed again until a visible result appears. The interaction between the acid and the "echo" of the original marking makes the latter stand out again with a color change. Such visible markings must be documented photographically as soon as possible – they do not remain permanent. As an example, consider a recovering mixture used by the New Jersey Police Laboratory in the 1950s: 40 cc of concentrated hydrochloric acid, 30 cc of distilled water, 25 cc of ethanol, and 5 g of copper chloride crystals. This method can be modified by current flow to an electrochemical process with higher sensitivity.
The core problem for gun collectors remains: the surface is now very badly damaged, i.e., abraded, polished and then etched. This also applies to existing coatings, regardless of whether they are blued, varnished or electroplated, such as nickel or chrome. This means that these methods of verifying counterfeits or searching for (value-enhancing) markings such as manufacturer's marks on antique firearms are almost pointless. Who wants holes or dents in the material and large flaws in the bluing or the surface that has patinated over centuries? It is hardly desirable to prove the authenticity of the piece to doubting fellow collectors, but then to charge a severe loss in its value. Even in forensics, non-destructive testing is desirable in order to preserve the integrity of evidence for further investigation that may be necessary later.
Non-destructive methods for testing a firearm's serial numbers and markings: the magnetogram
A remedy is provided by a method that shows the structural changes in depth not by the chemical route with acids, but by the magnetic route. The advantage for gun collectors is that coatings weaken the signal, but generally do not have to be removed because they are magnetically penetrated. The procedure is more precisely called "Magneto Optical Imaging (MOI)". The term "magnetic scanning" is more appropriate here. Settlement remains lying in the depths of the earth have long been found using this principle. The question is: how can this be used to recover an image of the markings of edged arms or firearms that are being searched for? Older readers remember the time before CDs and USB sticks and thus the magnetic storage of data on thin, long plastic tapes. If these only produced melodic tones, they were called a “audio cassette” or a "musicassette". The video recorder, which is almost extinct today, played music with moving pictures. The common feature of these devices is plastic tapes dozens of meters long with a coating of countless, magnetizable tiny ferric oxide particles. These are selectively magnetically aligned when the data is recorded. During the reading process, the alignment of the particles is detected by the tape head while the tape moves at a continuous speed along a sensor.
Damage-free inspection: example on "a Colt M1911 from the 1920s" using magnetic scanning
The examination of a supposedly original Colt M1911 pistol from the 1920s illustrates the immense advantages of magnetic scanning. Even the visual inspection raised some doubts. But the previous owners considered it a utility item, not a collector's piece. Small alterations that came about over the decades are often found on then not quite original, but still desirable and expensive pieces. Otherwise, ad oculos: very good, period condition, only the surface on the slide sides showed minor waves. However, these may well be due to the hand polishing required prior to nickel plating at the time of manufacturing. The detailed photos of the slide side show just how much a purely physiological look can be deceptive. Advances in technology have not stopped at tape heads either: in their modern forms, resolutions down to almost the individual ferric oxide particle are possible. This produces the detailed magnetic image of surfaces and their magnetic depth structure – the echo of the marking.
How the technique for restoring markings on valuable collector's firearms works using magnetic scanning
The frottage of a coin serves as a symbol: a sheet of paper lies on it and is rubbed with a soft pencil. The different relief heights of the coinage appear as an image on the paper. The magnetic tape serves as the paper and a rollable permanent magnet as the pencil. The magnetic changes in depth correspond to the embossing relief as information storage. For a magnetic scanning, reasonably clean and smooth surfaces are sufficient. In contrast to the mechanical-chemical method, magnetic scanning allows non-destructive examinations that can be reproduced at will. In addition to forensic clarifications, financially important examinations are also possible, such as for the authenticity of collector's firearms, their exact origin determination or their chronological assignment.
The magnetic tape is pulled once through the scanner's opening for preparation, thereby demagnetizing it. The tape is then fixed as flat as possible and in intimate contact with the surface to be examined. With the permanent magnet ("pen"), the examiner moves once lengthwise over the tape with light contact pressure. The magnetic strip is then inserted into the reader and – done! The highly sensitive magnetic reading head feeds the data directly into the laptop connected to the system, which immediately calculates the corresponding magnetic image of the examined surface.
If the application of the magnetic pen does not lead to meaningful images, it is possible to apply an AC magnetizing head or to fix the complete object in a stationary magnetizing station. This allows even better resolution, even with non-ferrous metals. The bad guy faction has long known that simple grinding is only enough to fool the unarmed eye. Extremely high-speed miniature grinders are now stocked by every hardware store. What could be more obvious than grinding or milling very deeply into the material? But the structural changes are up to two millimeters deep under the markings. Grinding this out goes into the depths of almost all relevant gun parts and can provoke fractures.
Besides the question of authenticity, gun collectors often wonder which factory – or manufacture – (really) made the new piece. Which Colt collector does not know the extremely value-increasing Singer marking on an otherwise standard M1911 A1? Corrosion damage or often preservable dense patina on antique firearms also often form obstacles to accurate chronological classification, but not to magnetic scanning.
Conclusion on the tested magnetic scanning device from Regula Forensics
Especially with additional devices, the presented methodology has meanwhile established itself as the state of the art, especially in the automotive sector. However, the price of the systems is an obstacle – the costs have so far been in the mid five-digit range. This is not exactly cheap, but when testing high-end collector's firearms – or those that could be – they definitely are worth the price. The manufacturer and distributor of the tested device is Regula Forensics in Düsseldorf.
Text: Götz Coenen and Robert Riegel | Photos and graphics: Götz Coenen, Wolfgang Dicke †