Target-UV™ & UV-Gray™
Target-UV™ is a calibration reference to control color and intensity of UVA induced visible fluorescence.
UV-Gray™ is used to set camera white balance using a variety of UVA radiation sources.
Both Target-UV™ and UV-Gray™ are made from stable inorganic pigments insuring accuracy and repeatability over many years of use. For more information on permanence of the Target-UV™ and UV-Gray™, see this paper.
The Target-UV™ increases the consistency and evidentiary value of UV/visible fluorescence images. This is achieved by the unique structure of the Target-UV™, which produces a neutral gray fluorescence when exposed to UVA radiation. The exact output of the fluorescence is dependent upon the radiation source used, allowing the Target-UV™ to adapt to different radiation sources. This allows for the creation and sharing of valuable data across cultural heritage institutions. These same benefits are now available for diverse fields, including forensic document examination and medical imaging.
Following a period of research and development, prototypes of Target-UV™ and UV-Gray™ were tested by select collecting institutions. This test highlighted the predominance of subjective and inconsistent approaches for the documentation of UV-visible fluorescence. Major differences in workflow, intensity and color reproduction, camera filtration, and post-processing were noted. Use of Target-UV™ and UV-Gray™ by the same group demonstrated that, with controlled workflows, these institutions could create images depicting UV-visible fluorescence that were objectively comparable, regardless of variables, including camera manufacturer and UVA radiation source. This work was presented at the AIC 42nd Annual Meeting San Francisco, CA in 2014. Read the postscript of this talk here.
As illustrated by early testing of the Target-UV™, human perception of fluorescence is highly variable. The reason for this variability is complex. Human vision and perception can differ based on age, gender and other factors. Throughout the development process, the benefits of interoperability and standardization were given precedence over inconsistencies of visual perception. For further discussion on this topic, see the FAQs.
The Target-UV™ is double-sided. Two intensity levels are present on each side: Low/Medium and High/Ultra. When used with the recommended workflow, the Target-UV™ is designed to reproduce intensity using the four tiered intensity levels on the Target, but also with tiered exposure. In this way, the images become accurate records of the intensity of the fluorescence in relation to the scale represented by the Target.
The design of the Target-UV™ provides overlap of the grey patches in each intensity level, allowing for comparisons and flexibility in exposure. For example, the lightest gray patch on “medium” set is the same as the darkest gray patch on the “high.” This reduces the possibility of choosing the “wrong” intensity level and allows for comparison with images taken adjacent intensities.