Detecting Frauds and Repairs
on Oriental Rugs with Ultraviolet Light

Philip R. Lichtman

From Oriental Rug Review, Vol. 15/6

Ultraviolet (UV) light is a basic tool of the fine arts and the forensic sciences, used primarily to expose repairs and forgeries. When a rug is repaired, or purposely altered such as by changing an inscribed date, the affected areas may show up strongly when viewed in UV light unless the worker has employed heroic efforts to disguise his or her endeavors. In Turkey, it is said, some repair shops use wool unraveled from old kilims in their restorations. To the extent that the old dyes match those in the rug under repair, UV detection may be difficult or impossible.

To understand the effects of UV light, a little technical background is in order. When we look at dyed wool, the impression of color results from the way the wool absorbs and reflects light. To make a color match, the repairer picks and (when necessary) mixes colors "in the needle" until the new wool gives the same impression of color as the old. One wool may have a little more green, the other a bit more blue and yellow, but overall the effect is almost identical. The method works because we can see the results.

Illustrations 1a and b. A skillful early repair on a Northwest Persian runner is detected by ultra-violet light.

However, UV light lies beyond the bluest light we can perceive and consequently can't figure into this subtle matching process. Any differences between the new and old wools' UV optical properties are obvious under UV illumination. There are plenty of these disparities between modern synthetic dyes and antique natural dyes, so it is usually apparent where recent work has been done.

If UV lies beyond the visible range, how can we use it for inspection at all? First, we can cheat. A so-called "ultraviolet lamp" usually emits quite a lot of near-UV light which, in the absence of the normal yellow and red rays, is capable of showing some contrast between new and old wools. Second, the real UV produced by the lamp may cause some dyes to fluoresce (absorb UV and reemit it as spurious colors), and wool dyed with these materials will stand out. Third, we can resort to photography -- either black and white, which is hard to interpret, or color, which is much more satisfactory. Photographic film, unlike our eyes, can "see" UV very well. In the developed film, the UV-rich areas show up in false colors. They aren't real colors -- remember, we can't see ultraviolet -- but all we need to determine fraud or repair are contrasting colors, and that's what the process gives us.

Illustration 1a shows a portion of a worn Northwest Persian runner before restoration. It was important to know how much work had been done previously. Earlier repairers had been skillful; it wasn't always obvious what was new and what was old knotting. Illustration 1b shows what the UV camera revealed. Looking to the right and left of the vertical center line of the rug, one can see major discrepancies. Large blocks of rug had been carefully re-piled.

This UV image gives a good idea of what meets the eye when a rug is bathed in the light of a commercial UV lamp in a darkened room. As mentioned above, the lamp puts out a lot of blue and violet visible light; otherwise we would see nothing except the fluoresced rays, if any. Thus Illustration 1b technically is not a UV photograph -- it is partially in UV and partially in visible light. Quite obviously this is good enough to make the alterations apparent.

Illustrations 2a and b. Extensive repiling on a yellow-field Lesghi or Kuba runner is revealed in the light of ultra-violet

Illustration 2a shows a yellow-field Lesghi or Kuba runner that has undergone extensive re-piling in which the color matches were done so carefully that the repaired areas are virtually undetectable from the front of the rug and are not always evident from the back. Illustration 2b is the same rug photographed in genuine UV, using a different method than in Illustration 1b. Full sunlight served as the illuminant, and a filter was placed over the camera lens to screen out all visible light. This filter appears black -- opaque -- to our eyes, but it is quite transparent to the UV camera. This is evident from the photograph, which has totally changed character vis-a-vis Illustration 1b. The repaired regions appear as light areas, rather than as the generally darker areas seen in Illustration 1b. The difference is that Illustration 2b is a true UV photograph -- no visible light is involved. (The low contrast of Illustration 2b isn't due to poor technique; it is inherent in true UV photography.)

It isn't always predictable how a rug will show up in UV light, so to do a thorough UV analysis of a rug it's wise to use both the methods described. In cases where fluorescence is a possibility, the method of Illustration 1b definitely should be employed, as the filter used for the method of Illustration 4 will block from the film any fluoresced light which is in the visible band.

It's necessary to state the following precaution: Never look at the sun through a UV filter. The image of the sun may appear very dim, but a big dose of searing UV will be hitting your retina. Permanent, serious, and immediate damage can result. Also, it is highly inadvisable to look directly at a UV lamp or the illumination it casts for more than a few seconds.

Surprisingly, the equipment needed for UV color photography can be relatively inexpensive although it takes considerable experimentation and technical experience to get good results. The typical indoor setup shown in Illustration 3 features a commercial mercury-vapor UV lamp which sells for a few hundred dollars. In a darkened room, this is ideal for visual inspection and for photographs of small portions of a rug. For large fields, more power is required, and multiple UV tubes can be mounted in standard fluorescent fixtures for this purpose. Alternatively, the method of Illustration 2b can be employed if the sun can be persuaded to cooperate.

Also shown in illustration 3 are two ancient Polaroid cameras, which in my opinion work better than the modern motor-driven Polaroids. These cameras are still available, reconditioned, for under a hundred dollars, and the copy stands are also obtainable. This setup was used for Illustration 2, the photo requiring an exposure time of about half a minute.

Illustration 3. The required equipment

Illustration 2b involved a 35mm camera on a tripod. Since the filter is opaque to the eye, it isn't possible to focus the camera or frame the field through the reflex viewer with the filter in place. Focusing and framing are therefore done before screwing on the filter. UV light comes to a focus at a slightly different point than visible light, and it may be necessary to experiment before good focus is obtained. Also, the automatic exposure control of a modern 35mm camera is useless for UV work; it will predict exposure times at wide variance with those required. Therefore it is advisable to use the manual mode, and sometimes exposures of several seconds are needed. Bracketing exposures over an absurdly wide range may obviate the need for a second "shoot".

For those readers who wish to try their hands at UV inspection, either visual or photographic, these notes may provide some guidance.

For those who don't want to bother with procuring the equipment and gaining the expertise, UV inspection is one of the services offered by the author's engineering company in Newton, Massachusetts. One may contact Philip Lichtman at 3 Valley Spring Road, Newton, MA 02158.