Some Special Observations Regarding Visible Transmission Spectra of Inks and an Improved Method for Their Discrimination by Microspectrophotometry

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Abstract
Various blue and black inks are shown to change their transmission spectra by applying pressure and smearing them as deposits on glass slides. A similar phenomenon is observed with deposits of copper phthalocyanine tetrasulfonic acid tetra sodium salt. It is shown that transmission spectra of small samples of inked paper fibers smeared (crushed) on glass slides resemble spectra of smeared ink deposits and are more reproducible than spectra of inked fibers in a mounting medium. This advantage is especially significant in the case of examining ink traces on tinted paper.