Infrared CCD, Infrared CCD reflected (IRCCDR) and Infrared False Color (IRFC)
The range of infrared light that is near the visible light spectrum and detectable with a common CCD camera is called IRCCD. In straightforward cases, IRCCD can reveal the underdrawing in a painting. Some pigments, such as lead white, become transparent with IRCCD. Generally, though, IRR is more effective than IRCCD. IRCCD and IRR are also useful in improving the readability of text in manuscripts that have been erased and overwritten.
How it works
Near infrared energy is the portion of the electromagnetic spectrum just past the red segment of visible light. Generally, the region between 780 and 1100nm is called IRCCD because a CCD and a slightly modified digital camera can detect this range.
False color infrared composites are generated by showing the green parts of the image as blue, the red parts as green, and the near infrared information as red. Therefore, two set-ups are needed in order to collect a visible picture (with RGB channels) and an IR picture.
|IR False Color||Channels|
|Red from visible image||G-green|
|Green from visible image||B-blue|
To shoot IRCCD images, you first need to modify your digital camera by removing the IR cut filter (http://www.astrosurf.org/buil/d70/ircut.htm). You then need an IR pass filter (under $100) to cut visible light, and an IR cut filter to take normal pictures. Common IR sources are halogen lamps and incandescent bulbs.
YOUTUBE VIDEO http://www.youtube.com/watch?v=R4hUFdwKDVQ
IR Reflectography (IRR)
What we learn
The term IRR refers to an imaging examination that uses devices which can detect far IR radiation to about 2 microns.
IRR is a powerful method to study the underdrawing technique used by an artist and greatly helps art curators authenticate pieces.
Renaissance artists used an underdrawing technique called ''spolvero.’’ They pressed a dust made of ground, powdered black chalk through the pricked outlines of an original drawing onto a fresh sheet of paper, leaving dotted guiding lines. Artists could then experiment with particularly important or complex parts of their designs.
Painters often drew sketches onto their canvasses, which they then ignored or changed. These are called pentimenti, and can be seen through an IRR camera. Finding pentimenti in a painting is often a proof of its authenticity. Indeed, an imitator doesn’t change his composition, whereas an artist often changes many details.
Hunting for pentimenti with infrared reflectography
Using only the light overhead, it would be impossible to look at the Virgin of the Rocks at the National Gallery in London and know that Leonardo da Vinci drew a hand under the Virgin’s face, and that there were many other figures that he never painted. But if you could see the image with an IRR camera, as in the image above, right, you would see the hand just below her mouth.
There are other numerous pentimenti or changes to the original design in the underdrawing, such as the alteration of the position of the head and legs of the Christ child and the position of the Virgin’s left hand. Finding these pentimenti has allowed scholars to conclude that the painting was not intended to be an exact duplicate of the first version of the Virgin of the Rocks, now at the Louvre.
How it works
Light in the IR spectral range to 2 microns can easily pass through most pigments, making the underdrawing visible. When an IR ray passes through the pictorial film and hits a black carbon line of the underdrawing, it is absorbed. When it hits the ground layer of white gesso (calcium sulfate), the IR light is reflected back. Therefore, the IRR camera "sees" underdrawing as a black area over white gesso.
These instruments look like common video cameras, but actually cost tens of thousands of dollars.