Fluorescence microscopy

Fluorescence microscopy is a technique which uses  an illuminating  ultraviolet light source and a system of filter to examine samples. The observable result is the fluorescence of the sample, which is visible to the human eye. 
Fluorescence microscopy is extremely useful in the study of multilayer samples. For example, this technique can be applied to artwork samples to make visible varnishes that do not appear when viewed with visible microscopy, and it can enable better visual separation of the color layers. 
In some cases it allows the identification of some pigments, such as zinc white, and it can also separate color layers which look similar when viewed in visible light.
 
Fluorescence
Occurs when a substance is excited by radiation, and reacts by emitting light at a wavelength longer than the radiation it received 

  • Microscopic sample of painted image under reflected visible light illustrated on the left - on the right, illustration of the same sample viewed under ultraviolet light. The intense yellowish fluorescence seen on the right picture is due to white of zinc, a pigment that was first used in the 19th century.
  • Painting sample under ultraviolet light. The white fluorescence of varnish is visible, and its penetration into existing microcracks apparent.
  • Sample of painted sculpture by Frosso Michaleas. On the left sample is shown under visible light and on the right under UV light. Observation of sample under ultraviolet resulted in the identification and recording of its upper layer of varnish, which give a mild fluorescence (No.8,) and showed that layer No.3 was deposited sequentially in three layers (3a, 3b, 3c). It also becomes obvious that while the two layers are black (No.3 and No.7) and resemble eachother, their different fluorescence showed they have different compositions.

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