Category Archives: U

UV fluorescence

UV fluorescence examination is a non-destructive examination method used on works of art. It uses UV radiation to make surface phenomena visible that remain hidden to the human eye in normal light. This allows important insights into the condition of the objects to be obtained, particularly in paintings for the visualization of varnish layers, retouching and overpainting. Occasionally, it is also possible to narrow down the material groups used (including binders).

The short-wave UV radiation stimulates the materials used (e.g. varnishes, binders, pigments) to fluoresce. The different fluorescence properties of the materials used allow a differentiated perception.

UV fluorescence photography should not be confused with UV photography or UV reflectography.

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The Universal Test Target (UTT) is a single test chart developed by the Dutch National Library (KB) in collaboration with Image Engineering Dietmar Wueller (IE) and the Fachverband für Multimediale Informationsverarbeitung e. V. (FMI) as part of the Metamorfoze initiative.

The aim was to design a new, uniform test chart that would incorporate the five standard test charts that had been in use until then and thus simplify handling. This was to provide an insight into the overall image quality of the scan results of all types of high-end cameras and scanners, based on current ISO standards. These are captured and analyzed with special software to provide information on technical aspects such as OECF, MTF, noise and color accuracy.

UTT is available in two versions: measured and unmeasured. The “measured” version comes with individually measured reference data for the particular chart purchased. The “unmeasured” version is produced in respect of the Metamorfoze standards and tolerances.

The UTT is available with a variety of options in sizes from DIN A3 to A0. Because the UTT is applicable to all types of digitization projects and preservation, it is particularly important for libraries, archives and museums.

The aim of the developers of the UTT was to save time and improve quality by using the unified target during the digitization process. However, it should be noted that the UTT is extremely error-prone in practice due to its simple design with individually affixed test charts and must therefore be handled with extreme care.

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UV light

UV light, also known as ultraviolet radiation or UV radiation, cannot be seen by humans, only felt. Probably the best known natural source of UV light is the sun. Artificially, UV radiation can be generated with the help of mercury vapor lamps and special light sources. UV light is divided into the three categories UV-A, UV-B and UV-C according to its wavelength. The short-wave UV-C light is largely absorbed by the ozone layer and thus does not reach our skin. The UV-B light makes it a little further, but is also rendered harmless by the cloud layers to 90%. UV-A light, on the other hand, is responsible for sunburn, eye damage, skin cancer and far more biological damage.

UV radiation can cause irreparable damage to sensitive works of art, especially works made of paper, such as prints, manuscripts or books. Depending on the duration and intensity of light, exposure starts biochemical processes that accelerate the organic aging process and lead to structural changes in paper, ink and paint. That is why we use only adjustable LED light units in our scanning systems for the most gentle illumination of the originals.

On the other hand, UV light (UV fluorescence) is used in the field of art science as an examination method, e.g. to make surface phenomena or faded inks on works of art, which cannot be perceived by the naked eye, visible by selective excitation with light of certain wavelengths. In this context, we use UV light exclusively in our multispectral system.

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In art history, especially painting research, underdrawing describes a preliminary drawing carried out by the artist, which is located directly on the primer of the picture carrier and is covered by one or more layers of paint. It can therefore usually not be perceived by the human eye. The term underdrawing is used to differentiate the more general term preliminary drawing, which also includes preliminary studies by an artist that were made separately on paper or cardboard.

Older paintings are mostly signed in some form. Art history distinguishes between two basic techniques:

  1. The scratching with a needle, as can be found especially in medieval paintings with gilded grounds

  2. The use of painting and drawing materials, such as those used for hand drawings, including graphite, charcoal, chalk, ink, Indian ink and white lead (opaque white)

The visualization of underdrawings harbors great potential for research in art history with regard to questions about the creation processes (work genesis), the materials used and the execution techniques as well as attribution and authenticity (original or copy).

Today, with the methods of multispectral photography, especially infrared reflectography (formerly also infrared photography), different layers and painting materials of a painting can be made visible and scientifically analyzed.

The book2net multispectral system also makes an important contribution in this area.


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