Examining paintings under UV light

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Benefits of Inspecting Art Work with an Ultraviolet Lamp

The Virgin and Child’ during cleaning. Under ultraviolet light, the old varnish at left has a greenish fluorescence
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The Virgin and Child’ during cleaning. Under ultraviolet light, the old varnish at left has a greenish fluorescence

Knowing what to look for

Ultraviolet light enables you to see evidence of imperfections, restoration and repair.  

Prior restoration can easily be detected through the use of an ultraviolet lamp.

In a darkened room, ultraviolet light (365nm) reveals alterations such as overpainting, repairs and floating signatures on artwork that is normally invisible in daylight. The slightest alteration will stand out with extreme clarity under UV light.

At 365 nm wavelength, many materials absorb invisible ultraviolet energy and transform this energy to visible coloured light, easily distinguished by the human eye.
 It is not reflected, but emitted light.

In some cases it is absorbed without emission, making these areas appear quite dark in contrast to the fluorescent areas. This makes an ultraviolet lamp an especially useful instrument in checking the condition of all forms of artwork.

When examining an oil painting look at the painting in a darkened room and view the artwork under ultraviolet light to see if any previous restoration has been done.

Using a hand held UV lamp is convenient and effective. You can easily scan the entire painting.

Dark blotches indicate repairs, floating signatures, over-painting and over- cleaning.

Bluish-white spots indicate the presence of lining compound, dark bluish-violet indicates picture repair putty and very small blue dots are dust.

A chartreuse haze indicates old varnish, which is what you hope to see, because it shows that no recent restoration work has been done.

Watercolour, gouache can vary in colour from pale blue to dark purple and orange. There is also a masking varnish that is used to hide restoration.

It has the ability to absorb the UV frequency but the surface has a greasy quality. The masking varnish is noticeable because of the density of the colour and the overall perfect coating of the varnish layer.

With paper art work bright areas show new patches of paper. Tissue and silking repairs are also clearly visible.

Smudged areas indicate rubbing out and very faint writing indicates erased signatures. New touch-up on watercolours and gouache has the same indications as on oil paintings. 

Old paper fluoresces faintly whitish, yellowish or gray but modern paper glows bright bluish white. Mildew (foxing) appears yellowish and makes water stains easy to recognize. Old vellum appears yellowish white or ivory, but modern vellum appears bluish white.

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