Art Terms Glossary beginning with U

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Ultraviolet fluorescence microscopy
An examination technique which uses complex optical microscopes to examine samples taken from an artwork at high magnifications using ultraviolet light. Many materials are identified by their characteristic autofluorescence; however special dyes (fluorochromes) are sometimes used to cause some materials to fluoresce in specific ways. This technique is very useful for documenting the layering of paints, varnishes and coatings in a section, enabling original materials and restoration layers to be distinguished and characterized
Ultraviolet light fluorescence
An examination technique which utilizes the characteristic of some materials to autofluoresce by absorbing the incident ultraviolet light and reemitting the energy at a longer (lower energy) wavelength. The intensity and color of the emission differs for various materials and can change as a material ages. Autofluorescence can help to visually distinguish between different materials, for instance, restoration paint often fluoresces differently from original paint layers. Fluorescence can also help to characterize materials using their autofluorescent colors, for instance shellac exhibits a distinctive orange fluorescence and madder (an organic red pigment) fluoresces bright red. Ultraviolet or UV light contains the portion of the electromagnetic spectrum with wavelengths ranging from 400-15 nm that occurs radiation occurs just beyond the violet (high-energy) region of the visible spectrum. Fluorescent light examinations are typically conducted using long wave UV light (400-320 nm) produced by black light bulbs or low pressure mercury vapor lamps.
Variations within the text of manuscript (calendar, litanies, etc.) peculiar to a diocese, town, or religious order. An aid to scholars in localizing a manuscript (Use of Paris).