Reflectance versus transmittance: The effects of light scattering on red colorants (carmine,amazonian red annatto,and peruvian cochinilla rojo and rosada) in biological,textile, and museum science |
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| Authors: | H J Swatland |
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| Affiliation: | University of Guelph, Guelph, ON, Canada |
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| Abstract: | Spectra were strongly influenced by the way they were measured but, in general, carmine, cochinilla rojo and rosada, and red annatto all had strong transmittance and reflectance of red light (>640 nm), and strong absorbance of green light (520–560 nm). Spectra for carmine and cochinilla rosada both had secondary peaks for transmittance and reflectance (around 420 and 450 nm for stains, respectively), whereas secondary peaks were not found for cochinilla rojo and red annatto. Both cochinilla rosada and rojo stained skeletal myofibers, but only cochinilla rojo withstood alcohol dehydration and mounting as a general stain for paraffin sections. Carmine was ideal for enhancing the appearance of pork because its spectrum was similar to that of myoglobin, thus increasing the absorbance of green light without producing unnatural colors like cochinilla rosada and rojo. Cochinilla rojo dyed alpaca wool orange, and cochinilla rosada dyed wool pink. The scale of the measurement (micro‐ vs. macroscopic) and the type of measurement (transmittance vs. reflectance) were of minor importance in colorimetry, whereas a major effect was detected for light scattering in the sample. A ratio indicative of scattering (400/700 nm) was strongly correlated with chromaticity coordinate x, r = ?0.86, P < 0.001, n = 18. © 2013 Wiley Periodicals, Inc. Col Res Appl, 39, 599–606, 2014 |
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| Keywords: | carmine cochinilla rosada cochinilla rojo annatto fiber‐optics |
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