ABSTRACT
This work used a multi-analytical approach to characterize two 19th century ambrotypes and was motivated by the lack of insight on these historical objects. Photographic imaging and optical microscopy (OM) were used to identify abrasions, cracks related to reticulation, tarnishing, and other aspects associated to production and degradation processes. With variable pressure scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (EDS) these processes were seen with great detail and further characterized. Elemental point analysis and elemental mapping showed that the photosensitive material used was silver iodide. Degradation compounds were found as silver and chlorine-containing compounds. In one of the items, the tarnishing area also contained redeposited silver in a ring-shape surrounding a nucleus rich in silver, copper, and sulfur, in addition to copper-based salts. EDS analyses also identified that the supports were common soda-lime-silica glasses, refined with arsenic; and showed that a pigment rich in iron was used in both items to hand color the cheeks, extended with aluminum silicates alone or mixed with barium sulfate. The µ-Raman study pointed out that a synthetic Mars pigment was employed. µ-Fourier-transform infrared spectroscopy analyses identified collodion as the binder. Shellac was used as a protective varnish in one of the items and a gum was possibly employed on the other. Bitumen was used for the background in one ambrotype.
ABSTRACT
We report here the draft genome sequences of two Brazilian strains of Cylindrospermopsis raciborskii, a saxitoxin-producer (CYRF) and a non-saxitoxin producer (CYLP), with each strain comprising one assembled scaffold. We revealed differences in the compositions of gene members coding for membrane transporters and antioxidant activities between the strains.
ABSTRACT
The degradation of indigo and its water soluble derivative indigo carmine was investigated under light excitation in the presence and absence of molecular oxygen in solution (homogeneous) and gels (heterogeneous) media. Collagen and carboxymethylcellulose (CMC) aqueous gels were chosen to simulate a natural textile environment, wool and cotton, respectively. Isatin was found to be the major degradation product of indigo. In solution, the photodegradation quantum yields (Phi(R)) were in the order of 10(-4), with the exception of aqueous media (Phi(R) = 9 x 10(-6)), and dependent on the irradiation wavelength. In the case of indigo carmine the Phi(R) values were found to suffer a 2-fold increase upon going from water to gels. The results indicate the absence of degradation products involving singlet oxygen and suggest peroxides, or other oxygen based radicals, to have a key role in the degradation of indigo. Finally, the relevance of the simulation is discussed by comparing the main degradation products to those found in the blues of millenary Andean textiles.
