Though science has its limitations in authentication, it has long been used to identify fakes and forgeries of everything from priceless paintings to baseball cards, Ming vases to advertising posters. This column looks at some of the more interesting and important methods and how they are used.
Ultraviolet light is one of the most used and useful tools for authentication and fake detection. Many collectors own black lights (the nickname for long wave ultraviolet light), and two previous columns showed how black light is used to authenticate sports cards (see here and here). Some of the biggest forgery cases have been solved in part due to ultraviolet light examination. This includes the infamous Hitler diary fakes of the 1980s and the forged photos of photographer Man Ray. Simple black light examination showed these forgeries were made with materials too modern for the subject.
Ultraviolet light is invisible to the human eyes, but when shined on a material the material will often fluoresce or glow in the dark. Different materials fluoresce in difference brightnesses and colors. The quality of the fluorescence originates at the atomic level of the material. The brightness and color will be different from material to material. The key is it can show qualities and difference in materials that are unseen under normal daylight.
Ultraviolet light covers a range of light frequency. The black light most collectors use is in the long wave range, while there are lights that give of shortwave light. For most collectors, the long wave black light is all they will ever need, but shortwave is useful in the areas of stamp, gems and fine art glass collecting. Shortwave ultraviolet light is somewhat dangerous, but safe to use if proper precautions are used including limiting use, not shining it directly on skin and eyes. Black light is safe, just don't look directly into the light source.
The following are just some of the other uses of ultraviolet light:
* Identifying alterations. The added glue, paper and other substances used in alterations and restoration will often show up under black light, as the added material fluoresce differently. Antique toys, iron banks and fishing lures are often identified as being repainted or revarnished in modern times because the paint or varnish fluoresces too brightly. Old paint and varnish tends to lose its florescence with time. Game used sports uniform experts identify alterations as the added cloth fluoresces differently than the original cloth. Even stitching can be identified as modern.
* Identifying art glass. The color of the ultraviolet fluroescence helps authenticate different kinds of valuable vintage glass. The color sometimes changes under long wave versus shortwave light.
* Materials identification. The color of ultraviolet induced fluorescence of many materials is knownand the black light can help identify the material. This includes gems, ivory and amber.
* Identifying fake watermarks. Many important historical documents and artworks are dated in part by watermarks in the paper. Real watermarks are a physical part of the paper, put in the paper during manufacture. Some people try to make fake watermarks but writing the design in mineral oil. These fake watermarks are usually clearly identified under black light as the mineral oil glows.
* Security marking. Many important objects, including Barry Bonds' record breaking home runs balls, are marked with invisible ink. The marks are invisible in daylight, but readable under black light. Some US paper currency has bands that are viewable under black light They also have bands viewable with infrared viewers. A black light is a useful tool for authenticating money.
Infrared is another frequency of light that cannot be seen with human eyes. The infrared camera and viewer translates infrared light into a visual image,
allowing humans to view details and qualities in the infrared range. With an infrared camera, you can take an infrared photograph. In fact, infrared photography is a popular form of art photography, as it gives a different, surreal view of the world. Unlike with black light, you don't shine infrared light on an object, but view what's already there.
The following are some uses of infrared viewers and cameras:
Infrared: Seeing Through the Paint
In the historical art and artifact world, infrared viewers are best known for their ability to view through the top layer of paint on a painted item. Art historians and museum conservators view through the paint to see any background sketches or earlier versions of the art. They do this to learn about how the painting was made and how the artist worked, planned and changed things. Studying the style and types of changes and background images is useful in determining if a painting was by a famous painter— his habits and techniques already being known. This process is referred to as infrared reflectography. Forgeries have been discovered because they were painted over paintings of modern subjects.
Reading heavily faded writing
Certain ink and pencil writing on old documents that have become invisible to nearly invisible in daylight can be sometimes be read in the infrared range.
Identifying foreign or fake materials
The added materials for restoration and other alterations can sometimes be seen in the infrared range.
An infrared viewer can help in identifying some items that have been repainted or touched up. The touched up area may be unnoticeable in visible light, but may stand out in the infrared range.
With art, collectibles and artifacts , X-rays are used in two different ways. One is the same x-ray examinations we get at the doctor's office, while the other is similar to how we use black light.
'See through' effect of X-rays
X-ray machines are used to examine paintings and other objects in a similar way they are used to examine human bodies. As with ultraviolet and infrared light, X-rays are a form of light invisible to human eyes. X-rays pass straight through some materials, but are reflected or absorbed by others. In the physician’s office, the X-ray machine shoots X-rays at the patient and has X-ray sensitive photographic film on the other the other side of the patient (Duly note that ‘film’ is an old-fashioned term and technology as even X-ray machines have hit the digital age). The X-rays pass through the patient’s skin and flesh and go to the film, but are absorbed by the bones. The result is the X-ray photograph shows the inside bones, allowing the doctor to examine the inside of the body.
Art historians get a similar insides look at paintings and artifacts as X-rays go through some paints, cloth and other materials but are absorbed or reflected by others.
For paintings, it often shows what was painted underneath the first level graphics we see with our naked eyes. Famous artists are known to have had standard ways and personal styles in how they constructed their paintings, which helps the historian in judging the authenticity, and some paintings started out as dramatically different designs. X-rays have shown that Picasso’s famous ‘The Old Guitar Player’ started off as an old woman instead of an old man, and an El Greco portrait started as a still life.
In x-ray fluorescence tests, x-rays or gamma rays are shined on the object. The atoms in the material are excited and in return give off a fluorescence. This is similar to the fluorescence given off under black light. The x-ray induced fluorescence originates at atomic level the material, and scientist measure the fluorescence to determine the chemicals and their amounts I the materials. When the chemicals are known, it can help date objects such as paintings, because it is often known when specific chemicals were used in say paint and other human made materials.
Radiometric dating is a highly advanced method used to date things from rocks to fossils to paintings. It was invented by legendary British nuclear physicist Ernest Rutheford, and University of Chicago professor Willard Libby won the 1960 Nobel Prize for physics for his work in the area. The best known form of radiometric dating is carbon dating, but there are methods using chemical other than carbon.
The scientific logic behind radiometric dating is straightforward. When something is living, certain chemicals are known to be in balance at a certain proportions to each other. When the thing dies, the chemicals decay but at different rates. Some chemicals decay very slowly, while other decay more quickly. For examples, the chemical rubidium has a half-life of 50 billion years, while carbon-14 (used in carbon dating) has a half-life of 5730 years, while lead-210 (used in dating of painted objects) has a half-life of 22 years. Measuring the current proportions of chemicals and knowing the rate of decay, scientists can accurately calculate the date of an object, whether it's a rock or a painting. Many paintings and artifacts have been identified as modern fakes or having materials consistent with being authentic via radiometric painting. Famous items that have been dating with radiometric dating include the Dead Sea Scrolls, the Shroud of Turin and the Mona Lisa. Though perhaps cost prohibitive, radiometric dating could be used for many vintage collectibles, even baseball cards and jerseys.
Thermoluminescence is an advanced scientific method to determine when an item was last heated, and is used to determine the age of vases and other human made objects. After a vase or other object is heated, the atoms of the material slowly attract energy from the surrounding environment. When a sample from the artifact is re-heated at very high temperature in a laboratory, the sample gives off the stored energy. The brighter the light given off, the older the sample.
Collectors and scientists use microscopes to get a closer look at items and sees details and qualities that cannot be seen with the naked eyes. Experts can identify the process and even age of photography and printing from the microscopic details. Many cheap reprints of trading cards or valuable advertising posters are easily weeded out under high magnification.
Physical examination of material samples
There are a variety of laboratory methods to identify the chemicals and other substances in paints, ink and paper. They involve taking and examining a small sample from the object. Paper chemists can determine the age range of photo paper because they know what kind of wood pulps and cloth were used at different times. Photo forgeries have been identified through examination of paper samples. Forensic ink experts can not only date certain inks but in cases deteriorate what brand of pen it came from. Many famous forgeries cases have been solved using these methods.
Dendrology, or the study of trees, has been used by art historians to help date many old paintings, and can be used on other wooden items. Before canvas, paintings were most commonly painted on panels of wood, and called panel paintings. The Mona Lisa, Botticelli's Birth of Venus and Hieronymus Bosch's The Garden of Earthly Delights are just three famous paintings on wood. Studying the rings in the wood and knowing when certain regional historical conditions such as draughts or fires caused abnormal rings, historians are able often able to determine the age and source of the wood for a painting. With the advent of this technique, historians have sometimes found that famous paintings in museums have long been mis-dated.
The limits of Science in Authentication
In art and collectibles, science can identify many fakes and forgeries, but has limitations in authenticating. For example, if a chemist shows that the paint and canvas used for an advertised ’1660s Rembrandt oil painting’ is from the 1800s, that proves beyond a doubt that the painting is a fake. However, if science shows the canvas and paint is from the 1660s, that doesn’t prove the painting is by Rembrandt. It could have been by a student or admirer of Rembrandt copying his style. The chemist’s finding is clearly useful towards determining a Rembrandt’s authenticity, but the authentication also requires art historians assessment of the painting’s style, quality and other non-scientific aspects.
Autograph forgers often forge signatures on old paper or baseballs, and authentication takes more than dating the paper and balls.
Further, physical samples, such as for paper fiber analysis and thermoluminescence, are taken from only a part of the object. When doing a thermoluminescence test on a vase, the sample is usually taken from the less conspicuous bottom. Forgers know this and will sometimes make a forgery on top of a broken ancient vase base, so a test from the bottom will come back as old. Similarly, if you make digital computer reprint of the front of the expensive 1909 T206 Honus Wagner card and paste it over, a genuine common T206 common card a sample will from the back will test as old.
Collectors and authenticators can't wear blinders and must take in all information. Relying on just one thing, one test, can lead to erroneous results. Use common sense.
Suspicions arise before tests are performed
For all famous forgery cases, there were general questions and suspicions about the items well before scientific tests were done. The scientific tests were done in response to questions from the collecting community.
Science is a supplement to, not a replacement of, old-fashioned collecting knowledge, observations, discussions. The experienced collector's eye and well read mind are two of the best authentication tools.
Science is constantly moving forward
As science advances, more current fakes will be scientifically identified. Fakes that fool people today will be identified tomorrow. Gives new meaning the term 'lifetime guarantee of authenticity.' In fact, much forensic research has been done in response to questioned items.