Below are examples of multispectral image overlays – a technique used to illustrate even subtle differences between images of a painting taken using varying imaging techniques. A multispectral image is produced by overlaying and aligning two images, each having been taken using one of a variety of analytical methods such as Ultraviolet Fluorescence, Ultraviolet Reflectography, Visible/Raking Light, Infrared Photography, Infrared Reflectography and Transmitted IR. ArtGenomics offers all of these techniques, along with the multispectral images made possible by them.
Visible Light vs. IR Photography
Image: Detail – Isabella Brandt by Sir Thomas Lawrence – copied after the original by Peter Paul Rubens in the Uffizi Gallery, Florence. Oil on Canvas, circa 1820.
Infrared light is transmitted or reflected by materials at different rates depending on their constituent matter. Certain paint pigments, both organic and mineral, respond better for art historical purposes (i.e. are more transparent) to IR light of the correct wavelength. The aim in IR analysis is to penetrate through the surface paint layers to show changes to a painting that are no longer visible to the human eye. IR is particularly useful in the study of charcoal underdrawing, as even light in this portion of the spectrum is absorbed by charcoal and other darker compounds, allowing them to be seen in contrast to the more reflective ground layer beneath. This allows for examination of any underdrawing if present, including pentimenti (changes to the conception of the painting). In the above comparison, the IR image reveals charcoal and wash underdrawing, along with fine craquelure and minor surface abrasion. There are no clear changes to the sketch, which is often the case for works such as the above, which has been copied from the original. Such information can be used to assist in identifying the author of the painting, the artist school or period, or to assist in a conservation assesment.
Image: Transmitted infrared image of an inscription hidden beneath a new canvas lining on a 17th century oil painting. The image reveals the date of creation and identity of the sitter, both previously unknown. NB* The format of this image has been reversed in order to present the hidden text more legibly.
Visible Light vs. UV Fluorescence
Image: Portrait of Lady (thought to be Sofonisba Anguissola) by Sofonisba Anguissola. Oil on Canvas, circa 1610.
UV Fluorescence is a technique used to observe the foremost layer of a painting. This layer often consists of varnish and any retouching or in-painting. Organic varnishes fluoresce under UV light of the correct wavelength, and recent additions of paint will appear dark and clearly defined. Damaged areas, as well as those which have been rubbed down or cleaned, will fluoresce less intensely, if at all. The above image comparison illustrates a phenomenon know as “key holing” in which a painting is cleaned primarily in the area of the face (and sometimes other detailed passages, such as hands) in order to freshen the appearance of the portrait. In the above instance, the observable key holing is likely the result of careful conservation work. Darker areas of the painting, in particular those shaded black, are more susceptible to damage when cleaned so are often treated with caution, or left alone. The cause of this instability of dark pigments is a compound called bitumen (also known as tar, or asphalt), which was frequently used by artists as a black pigment when dissolved and mixed with oil/wax.
Hi-Resolution Visible Light Imaging
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Portrait of two boys (1986) – By Arthur Shilling
Art is extremely difficult to photograph accurately. This is especially true of paintings with heavy and discoloured varnishes applied to them. A quality image once captured however, is an invaluable asset to the owner of the artwork in question. ArtGenomics employs museum quality imaging techniques for the highest standard of visible light photography. Images are true-colour balanced, evenly lit, exceptionally sharp, and contain low surface glare/diffuse reflection, allowing for an extremely accurate visual analysis of an artwork via photograph. Such images are highly valuable to art owners looking to authenticate, sell, catalogue or publish a work in their collection.
In addition to true colour HD images, AG offers macro imaging for 1:1 analysis of paint surface details such as signatures, alterations, and finely painted passages. Details such as these can be useful for both conservation and connoisseurial purposes.
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