Use UV lamps to inspect museum collections
Ultraviolet radiation is invisible to the naked eye, but when the ultraviolet light emitted from the ultraviolet lamp is directly irradiated on the surface of the collection, it can be transformed into visible fluorescent light with visible colors, which is visible fluorescence caused by ultraviolet light. Therefore, UV lamps can be combined with other inspection techniques to help museum managers determine the preservation status of the materials and cultural relics in the collection.
However, in recent years, there has been very limited research on museum collections exposed to ultraviolet lamps to inspect museum collections, but the cumulative effects of artificial ultraviolet light sources and natural sunlight on museum collections, as well as the problems that cause damage to collections, such as Research on the fading of fabric collections, paper collections and other organic materials is more common. The collection absorbs very limited ultraviolet light during a short inspection with an ultraviolet lamp. If the inspection method using ultraviolet rays can diagnose the problems in the collection, then this technique is still acceptable.
1. About the electromagnetic radiation spectrum Ultraviolet rays, visible light, infrared light, radio waves, X-rays, and gamma rays and cosmic rays that are not familiar to everyone are all forms of electromagnetic radiation. All forms of electromagnetic radiation are divided according to wavelength, which is measured in nanometers (nm), which is one billionth of a meter. Visible light is only a part of the electromagnetic spectrum that is visible to the naked eye. The wavelength of visible light is between 400-700 nm. The wavelength of ultraviolet light is shorter than that of visible light, between visible light and X-rays. The composition of ultraviolet light in the electromagnetic spectrum can be divided into the following parts:
UV-A is called long-wave ultraviolet, near ultraviolet, black light, etc., with a wavelength between 320-400 nm
UV-B is medium wave ultraviolet (280-320nm)
UV-C, commonly referred to as short-wave ultraviolet, far ultraviolet, or germicidal ultraviolet (180-280 nm)
2. Visible fluorescence induced by ultraviolet rays Many natural and synthetic materials can convert ultraviolet light into visible light with a longer wavelength. This phenomenon is called ultraviolet-induced visible light. After the object is absorbed by ultraviolet rays, the electrons enter a higher energy state, and the absorbed radiation is released again when the electrons return to the normal state. This released radiant energy is fluorescence, which appears in the wavelength range of visible light. , So it can be observed with the naked eye. The material being inspected exhibits different colors (fluorescence at a specific wavelength) when it fluoresces, depending on the material being inspected and the ultraviolet wavelength used.
3. Examine artworks and cultural relics. Use ultraviolet lamps to inspect collections. Choose a dark room, such as a storage room or dark room. Because the fluorescence is not very bright, look for dark places as much as possible to avoid light coming in through windows and doors. Windows can use blackout curtains. Turn on the ceiling lamp or work desk lamp, and place the collection to be checked on the table or easel. Plug in the power supply of the UV lamp or check the battery of the UV lamp. Make sure that the wires do not get tangled together, do not trip the operator or cultural relics, and make sure that there are no obstacles when handling the collection in the dark. Turn off the lights in the room and let your eyes get used to the dark environment for 1-2 minutes. Observe the collection under ultraviolet radiation. The collection will not show fluorescence in a completely dark environment. The surface of some non-fluorescent substances ( Such as metal) will reflect a small amount of visible light leaking from the UV lamp. Be careful not to confuse this light with fluorescence.
Under ultraviolet radiation, do not try to relocate, clean, inspect or make other changes to the collection. These can only be done after the room lights or work lights are turned on. UV light can only be used for inspection.
The color of the fluorescence observed depends on the material and the wavelength of the ultraviolet rays used. For example, many glues used to repair cultural relics fluoresce under long-wave ultraviolet rays, but they do not react at all under short-wave ultraviolet rays. Therefore, long-wave UV is used to measure damaged or repaired ceramics. At the same time, many mineral specimens emit fluorescence under short-wave ultraviolet radiation, but not under long-wave ultraviolet radiation. Therefore, short-wave UV lamps are helpful for the classification and cataloging of collections.
As with other inspection or analysis techniques, it is not possible to draw conclusions based solely on UV-induced visible fluorescence inspections. It is best to combine other evidence about the collection for analysis. Special care should be taken in the authenticity of cultural relics.
4. Fluorescence characteristics of artworks and cultural relics (1) The long-wave ultraviolet inspection of oil paintings can reveal the natural gum varnish layer. Natural gums will fluoresce and appear yellow-green mist on the surface of the oil painting. Some other varnishes, especially those containing linseed oil, will show a blueish haze-like fluorescence. If the oil painting has been repaired in the past, it can be reflected through the fluorescent display. For example, if the varnish is selectively removed from a location on the screen, then this part of the entire fluorescence reflection will be missing. Later, it was added that the fluorescence of the material was darker than that of the original oil paint and varnish, or there was no fluorescence at all. Therefore, usually appear black or dark areas on the screen.
The re-repaired layer may be above the early varnish layer and below the later repair layer. In this case, it will also show fluorescence. When checking the oil painting collection, the fluorescence emitted by the medium of the oil painting is very bright, so the image of the oil painting is easy to see. A few pigments (colorants and oil painting materials mixed together) will also fluoresce and show unique colors, which can prove the pigments used. (For example, zinc white pigments fluoresce bright lemon yellow.) No fluorescence does not necessarily indicate that the surface varnish has been removed. Dust or dirt on the surface will greatly reduce the fluorescence. Moreover, many synthetic gums do not fluoresce at all. Unlike most acrylic paints, most acrylic paints do not fluoresce. In the oil paintings of the first half of the 19th century, the black spots under ultraviolet light were later repaired.
(2) Ceramic and glass ultraviolet rays are most commonly used to check ceramics and glass. You can check whether they have been repaired before. Many adhesives used to repair ceramics will have fluorescent rays at the repaired place under long-wave ultraviolet irradiation, and these adhesion The fluorescence of the agent is more obvious when aging, which is in sharp contrast with the place where no fluorescence is generated. These adhesives show various colors of fluorescence under long-wave ultraviolet light, such as epoxy adhesives show bright yellow fluorescence, polyethylene adhesives such as Elmer glue show blue fluorescence, shellac shows bright orange fluorescence. The cellulose acetate binder exhibits milky white fluorescence, and the nitrocellulose binder exhibits yellow-green fluorescence. However, there are some adhesives that do not fluoresce under ultraviolet light, such as the acrylic resin Acryloid B72®, which is commonly used by ceramic restoration experts to repair ceramics. Therefore, not all repairs can show fluorescence under ultraviolet light.
UV inspection also helps to find places in the collection that have been replaced, such as repaired filling on ceramics, etc. It usually shows fluorescence under long-wave ultraviolet, which is in sharp contrast with the darker places that do not emit fluorescence.
Hard pottery can be identified by emitting pink under short-wave ultraviolet light, while young pottery shows milky white fluorescence under short-wave ultraviolet light. Lead-containing glass exhibits a small amount of fluorescence under long-wave UV, but bright blue fluorescence under short-wave UV, and glazed glass exhibits bright yellow or green fluorescence under long-wave UV.
(3) The fluorescence of marble, limestone, and alabaster that is just cut from the stone is not obvious, but as these stones age, a layer of covering will be formed on their surface, showing mottled white fluorescence under long-wave ultraviolet light . This characteristic is often used to identify old marble, limestone and alabaster, to distinguish it from newer stone materials that have been artificially aged. This technology is of low use value for other stone materials, such as granite and sandstone, and their aging methods are different from the above-mentioned stone materials.
Like the inspection of ceramics and glass, the UV inspection of stone artifacts helps to identify whether it has been repaired before. Because the use of adhesives usually fluoresce and show signs of repair. Places filled with different materials, such as places filled with gypsum or wax, show different fluorescence from the surface of the stone material.
(4) Ivory and bone relics The fluorescence of ivory and bone under ultraviolet light is similar. Under long-wave ultraviolet light, they show bright white fluorescence when they are newer; if they are older, they will show soft and mottled yellow fluorescence. Repairs on aged ivory and bone artifacts can be done in the same way as described above for the inspection of ceramic, glass and stone artifacts.
(5) Metal Metal usually does not emit fluorescence, but materials used for surface treatment of metal materials, such as wax and resin, emit fluorescence. Some waxes will show bright white fluorescence under long-wave ultraviolet radiation; the fluorescence emitted by natural gums is green, yellow, or light gray. Synthetic gums are usually used as coatings to prevent the corrosion of cultural relics, and may not necessarily emit fluorescence. Therefore, the absence of fluorescence does not indicate that these artifacts are not coated. As for the artificial aging by applying other paints and glazes on the surface of metal artifacts, it can usually be identified by ultraviolet inspection.
(6) Paper and parchment paper Modern paper is added with fluorescent whitening agent, so it shows bluish white fluorescence under long-wave ultraviolet light, and older paper usually shows white, yellow or gray fluorescence. Through this feature, it can be used to distinguish the age of paper. Mold on paper and parchment is invisible under visible light, but it can be found with long-wave ultraviolet light.
Under the ultraviolet light, the mold will show a yellowish fluorescence. The repair marks on the paper and parchment are easily recognized under ultraviolet light. The place on the paper that has been replaced and any method used to strengthen the strength of the paper, such as the backing, are usually different from the original.
(7) Textiles The old textiles and new textiles can be distinguished by a method similar to the identification of old and new paper. Modern textile threads are usually treated with fluorescent brighteners, which emit bright fluorescence under long-wave ultraviolet irradiation. The repair marks on the fabric can be distinguished because the fluorescence emitted by the repaired area is brighter, while the original material emits less fluorescence or does not emit fluorescence at all. However, ultraviolet light must be used with great care when inspecting textiles, because old fabrics, if they have been cleaned with modern cleaners, will be attached with optical brighteners, resulting in errors in the inspection results.
(8) Wood Although some types of wood (such as sumac) emit strong fluorescence under long-wave ultraviolet radiation, most newly felled trees rarely emit fluorescence. Only after a long period of time, the surface of the wood is Under the long-wave ultraviolet radiation, it showed mottled fluorescence. Wood materials that have been repaired and have undergone artificial aging treatment usually do not emit fluorescence, and can be distinguished by comparing with the fluorescence emitted by old wood.
Fluorescent coatings and varnishes on wood surfaces can also be judged by ultraviolet-induced fluorescence. Commonly used wood paints and shellacs will emit special bright orange fluorescence under long-wave ultraviolet light.
(9) Mineral specimens Most gemstones and mineral specimens emit fluorescence, and many emit fluorescence under short-wave ultraviolet rays. Fluorescence is often used to classify these materials, determine their origin, and their constituent materials. Minerals that fluoresce under short-wave ultraviolet include: scheelite usually exhibits blue-gray fluorescence, and berylite exhibits strong orange-yellow fluorescence.
Fifth, how to choose an ultraviolet lamp When choosing an ultraviolet lamp, many factors should be considered to determine which material is most commonly used for inspection, so as to decide whether to buy a long wave ultraviolet lamp (LEA-160L) or a short wave ultraviolet lamp (LEC-160L), Both long-wave and short-wave UV lamps (LEAC-260L), choose whether to use a socket or a portable UV lamp according to your needs. The handheld UV lamp (LP-365D or LPX-365) is suitable for places where there is no power outlet in the workplace, but it must be recharged frequently or the battery should be replaced.
Another issue to consider is the type of lamp. There are two different types of lamps, high-pressure mercury vapor lamps and fluorescent lamps (or low-pressure mercury lamp). Fluorescent tube lamps have many modes, most of which are not expensive. More are mercury vapor lamps, which can emit high-intensity ultraviolet light, but heavier transformers are also more expensive, and there are also models that can be handheld. They are usually more bulky than fluorescent tubes, and there are few models to choose from. Moreover, it generates more heat energy than fluorescent tubes, so it can not be long and the time is too close to the surface of the cultural relics. However, because their output UV output is large, the fluorescence they generate is brighter and easier to observe. Compared with most fluorescent tubes, they have better filterability, so they will not leak visible light to the cultural relics being inspected, which further improves the visibility of fluorescence. The intensity of the lamp should also be taken into consideration. Intensities are measured in microwatts per square centimeter. Manufacturers usually list the intensity of fluorescent tubes. At 6 inches away from the surface of the object being inspected, the intensity of the ultraviolet lamp of the fluorescent tube ranges from 300 microwatts per square centimeter to 900 micrometers. Watts per square centimeter. The intensity of mercury high-pressure lamps is usually measured 15 inches away from the surface of the object being inspected. The intensity of these lamps ranges from 1200 microwatts per square centimeter to 6000 microwatts per square centimeter. Intensities within this range can meet the needs of routine inspections, although higher intensity UV lamps can produce brighter and easier to observe To the fluorescence. When buying UV lamps, remember to buy eye protection glasses. Long-term exposure to UV rays can cause serious vision problems.
6. Long-term exposure to ultraviolet light in the operator's safety issues can cause severe irreversible visual damage, including the deterioration of cataracts, glaucoma, and retinal spots. Therefore, wear LUV-10 UV protective glasses or LUV-40 UV protective masks throughout the inspection process using UV lamps. Especially when using UV-C (Short Wave Ultraviolet), more attention should be paid, because this ultraviolet rays are the most harmful to human eyesight and skin. It is recommended to use the LUV-40 UV protective mask designed to filter UV rays.
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