portable and easy to use even on high scaffolds required to reach mural paintings on
ceilings and high walls. The relatively low cost of equipment (depending on the
spectral range and resolution) also contributes to the widespread of the technique.
16.3.1 Microfading Tests
Measuring methods described so far and their interpretations were used for
chemical identification of components of the tested object. They could allow discovering the secrets of the artist’s techniques, serve for its dating or authentication,
point to the presence of degradation products, and allow assessing the threats to the
durability of the artwork. Knowing the chemical composition of dyes and/or pigments used by the artist, one can try to conclude about its resistance to environmental factors, in particular—to light. Knowledge about the ease with which a
given compound photodegrades, obtained in tests in an isolated system, does not
translate directly into the durability of the objects in which it was applied. The same
dye on different substrates may show very different lightfastness as is shown and
discussed in the example below (Fig. 16.8).
The two main goals of museums, archives and libraries, are to share and protect
the collection. The simultaneous implementation of them creates an antinomy—
light, necessary for the viewer’s contact with the work, is also a factor that causes
its degradation. The compromise that museums use, based on observations and
research results, involves the use of the smallest possible doses of light, which are
believed to not cause degradation for a given category of the object. For objects
considered to be the most sensitive, it means the need to reduce the radiation power
of light sources to the lowest acceptable level and shorten the total time of illumination (e.g., by periodically turning off the display or installing a proximity
switches) controlling in this way a total dose of light. Both these measures limit the
viewer’s contact with the work—for most people, the ability to recognize the colors
and details of the drawing in lighting at the 50 lx level recommended in such cases
is already significantly limited (especially for dark objects and objects with a low
contrast).
The solution that would allow for individual adjustment of illumination to a
given object could be to conduct photostability-accelerated aging tests with the use
of light source with spectral power distribution similar to the one used on exhibit.
Standard photostability tests lead to irreversible destruction of the sample, and in
the case of works of art and heritage materials, only a noninvasive (i.e., not
requiring a sample from the object) and non- or microdestructive methods could be
accepted. Determining here what microdestructive testing means in the context of
art analysis is not easy and will never be unambiguous. If the change in the object is
not perceptible to the human eye and does not affect its strength parameters, then
such a test is usually considered acceptable. In the case of microfading tests
described below, this condition is usually met.
502
T. Łojewski and B. Łydżba-Kopczyńska
ceilings and high walls. The relatively low cost of equipment (depending on the
spectral range and resolution) also contributes to the widespread of the technique.
16.3.1 Microfading Tests
Measuring methods described so far and their interpretations were used for
chemical identification of components of the tested object. They could allow discovering the secrets of the artist’s techniques, serve for its dating or authentication,
point to the presence of degradation products, and allow assessing the threats to the
durability of the artwork. Knowing the chemical composition of dyes and/or pigments used by the artist, one can try to conclude about its resistance to environmental factors, in particular—to light. Knowledge about the ease with which a
given compound photodegrades, obtained in tests in an isolated system, does not
translate directly into the durability of the objects in which it was applied. The same
dye on different substrates may show very different lightfastness as is shown and
discussed in the example below (Fig. 16.8).
The two main goals of museums, archives and libraries, are to share and protect
the collection. The simultaneous implementation of them creates an antinomy—
light, necessary for the viewer’s contact with the work, is also a factor that causes
its degradation. The compromise that museums use, based on observations and
research results, involves the use of the smallest possible doses of light, which are
believed to not cause degradation for a given category of the object. For objects
considered to be the most sensitive, it means the need to reduce the radiation power
of light sources to the lowest acceptable level and shorten the total time of illumination (e.g., by periodically turning off the display or installing a proximity
switches) controlling in this way a total dose of light. Both these measures limit the
viewer’s contact with the work—for most people, the ability to recognize the colors
and details of the drawing in lighting at the 50 lx level recommended in such cases
is already significantly limited (especially for dark objects and objects with a low
contrast).
The solution that would allow for individual adjustment of illumination to a
given object could be to conduct photostability-accelerated aging tests with the use
of light source with spectral power distribution similar to the one used on exhibit.
Standard photostability tests lead to irreversible destruction of the sample, and in
the case of works of art and heritage materials, only a noninvasive (i.e., not
requiring a sample from the object) and non- or microdestructive methods could be
accepted. Determining here what microdestructive testing means in the context of
art analysis is not easy and will never be unambiguous. If the change in the object is
not perceptible to the human eye and does not affect its strength parameters, then
such a test is usually considered acceptable. In the case of microfading tests
described below, this condition is usually met.
502
T. Łojewski and B. Łydżba-Kopczyńska