Category Archives: U

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.


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.


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