14 "der detektiv" September 2005

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So-called rubber stamps,although these are actuallymade of silicone and othersimilar materials, are stillwidespread both in businessand private life. But how doesone distinguish genuinerubber stamps from fakes andwhat are the techniques thatforgers use to make forgeries?Such problems are commonlyencountered by privateinvestigators who often haveto deal with cases involvingforged papers and who knowat least the basics of the trade.Nowadays it is no big deal tocreate a brand new duplicateof a rubber stamp withcomputer technologies thatare both accessible andprevalent in every high street,but most forgers still use oldtechniques that are far fromsophisticated. One of theoldest is the so-called potatotechnique, widely used byresistance movements duringthe Second World War in

Rubber stamps:fake or genuineHow to distinguish the fake and the genuine

Andrej Dvorsak *

Europe, and also in Naziconcentration camps. InEurope the ‘potato technique’is still in use.The forger boils the potato (nottoo much), and then cuts itdown the middle. One part ispressed on the genuine rubberstamp on the originaldocument for a few secondsto produce a ‘picture’ of therubber stamp print on the half-boiled potato. The potato isthen pressed on to the fakedocument. The result is arubber stamp print with thesame shape as the original,but much brighter with anunclear picture and shapes.You can distinguish the genu-ine and fake by their colors,which are thicker (morecondensed) on the genuinestamp. Also the lines andshapes are much sharper onthe original document. Underthe microscope you can alsousually see some stains ofstarch on the surface of thedocument. The starch can alsobe detected in a laboratory.The same procedure has alsobeen employed by forgersusing a fresh apple instead ofa half-boiled potato, and theegg technique was alsopopular among forgers. Theyboiled an egg, peeled awaythe eggshell and rolled the ori-ginal rubber stamp over thegenuine document. Then theyrolled the imprinted egg overthe fake document to establisha fairly good picture, which

was always very bright but withpoor shapes, on the paper.A more sophisticatedtechnique is to engrave theshapes of the original rubberstamp in flat wood, slate,plastic and others hardmaterials. These fakes can bedistinguished very easily fromthe original. In most cases thefalsifier presses the engravingwood or plastic too strongly onthe document so that underthe microscope the relief of thestamp can be discerned –which is not the case for origi-nal rubber stamps which alsotypically give quite differentshapes of lines. Moreover, thedifferent shapes and sizes ofengraved letters and picturescan lead to the conclusion thatthe stamp has been faked.However, the most delicateand hardest to prove aredocuments forged by moderntechniques used onphotocopies (Photostatsdocuments) and ondocuments »received« bytelefax machines. Thetechnique is very simple.The falsifier makes a scan ofthe original rubber stamp or aphotostat of it on a transparentfilm. Then this film is put overa document, so that the stampis positioned on the properplace. After that no specialefforts are needed to finalizethe forged document; all thatthe falsifier has to do is to pushof the button on the telefax orphotostat machine. The faked

* Andrej Dvorsak is a licensedprivate detective, licence 047, andthe expert for document andhandwriting analysis from Ljubljana(Laibach), Slovenia. He is theauthor of several books andscientific articles, among them thefirst Slovenian manual for privatedetectives. His contact address:contact: Andrej Dvorsak,Posavskega 5, SI 1000 Ljubljana,SloveniaPhone + 386 1 568 51 00http://www.detektiv-da.siE-Mail: da047@siol.com

"der detektiv" September 2005 15

○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○ ○Rubber stamps

document and the layer (film)with the pre-copied stampmake he get only onedocument, on which containsare all the details on theirplaces. Even an expertcannot, either with unaidedeyes or with a usualmagnifying glass, distinguishthe genuine from the forgedphotostat »faxed« document.Details, which show that therubber stamp is forged, are:• Colors are usually verybright• The shapes of lettersand pictures are not sharp,they are blurred instead• Proportion betweenletters and other details of thestamp are different from thosein the original• When the stamppartially covers is over thepicture or something alike, thestamp could be slightly moved,so that the lines of it are brokenon the edges of the picture andthe background foundationetc.For all these first steps on thefield of examination a PI needsonly a good magnifier and ahandful of UV light. In the laba document can be examinedunder the different types of UVand IR light, with microscopesand by means of various othertechniques includingmicrophotography, computerscans, chromatography etc.,but these are is lab and not PItechniques.PHOTOSIn my practice I had to checkthe diploma degree of theUniversity in pristine – Kosovo.The local contact send me thedocument from the University.On first glance ofinexperienced eye all was OK,including rubber stamp. Butthe expert can see somecharacteristics even withnaked eye and under themicroscope and otherinstruments thischaracteristics became visib-le also to everyone else. With

The stamp was suspicious alsoon first glance, because it has noclear number and the name offaculty is missing.

Under the microscope, here weused 17x magnification, you candistinguish fake and genuine alsoby lines, which was made by inkjet printer. Genuine rubber stampshas no such lines even under themicroscope.

Detail under the 64x magnification

Sometimes it is necessary tocheck the document also with dif-ferent types of light. This picturewas made under IR illumination.

Same part of the document madeby UV light from behind thedocument

Same part of the document, butwe used side light under verysharp angle

Same part of the document underthe normal (North) light

computer technique you canforge a document and rubberstamp almost perfect, butcomputer is not a friend ofcriminals and always left visib-le trace of the forgery.

(all pictures: archive of A.Dvorsak, made with VSC 2000in Forensic lab of SlovenianMinistry of Interior)