Image Processing Reference
In-Depth Information
Figure1.21 Visible (400-750 nm), NIR (830-1100 nm), and SWIR (1400-1700 nm)
images of a test panel with oil paint swatches and underdrawing media. Paint swatches from
left to right: burnt umber, burnt sienna, raw sienna, and ochre. Underdrawing media from
top to bottom: silver, ivory black, lamp black, vine black, charcoal in gum arabic. (Courtesy
of FLIR and LACMA).
The Dutch artist Salomom van Ruysdael drew an interesting underdrawing on
one of his paintings that is almost a scribble and very different in nature to the end
product. Figure 1.22 shows a painting of his calledLandscapewithDeerHunters
imaged in both color visible and SWIR light, with the details from the lower left
of the painting. Ruysdael drew loops (probably with a lead pencil) to suggest
foliage around the tree, and zigzag lines to delineate the landscape. We know that
Ruysdael used underdrawing in his early works—other landscape paintings from
this period (1630s) show similar underdrawing beneath the paint, but he stopped
using the technique later in his career. The figures are all drawn without the use of
underdrawing.
Subsurface analysis is especially valuable in the antiques market, which
contends with many forms of deception. Many pieces of antique furniture are sold
as being unrestored, when in fact they have sometimes been quite extensively
modified. A very common example of this involves repairs to wood veneers.
Veneers were attached to a substrate of heavier, stronger wood using animal glues.
Over time this glue can weaken, creating loose pieces of veneer that can get torn
off over the years. Figure 1.23 shows a piece of mahogany that has been veneered.
A repair made to the veneer panel was done with wax filler and then cunningly
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