| 摘要 |
It is known that minimal yellow casts, which can be detected with the naked eye only with difficulty, reduce the value of diamonds to a substantial extent. A reproduction method is described in the case of which colour photographs of the diamonds are produced in such a way that the wavelength region between 415 and 515 nm is suppressed and the intensities of the regions situated on either side of this interval are matched to one another. The blue-sensitive layer of the emulsion is thus stimulated only by light, the diamonds having a very strong self-absorption which cannot, however, be perceived by eye, because it is no longer sensitive in this wavelength region. The yellow cast is amplified by a factor of approximately 10-15 on the colour photograph, and is therefore very clearly to be seen. Moreover, calibration patterns which are photographed at the same time permit quantitative assignment to the different stages of the graduation scale.
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