"Pompeian red is really special. It represents the height of the ancient Romans’ mastery in making colors," said Daniela Daniele, a researcher at Berlin's State Museum. That unique quality makes it all the more important to learn how to preserve Pompeii’s brilliant red pigment.
They used an unusually fine grind (2~3 µm), which makes the pigment’s color more intense. They also mixed in larger crystals 10~15 µm, which gave a shiny quality to the surface. Cinnabar that is processed in the typical way yields a dull red similar to red ochre.
Artificial Atoms
Jim_Kling
Image Courtesy: PlasmaChem GmbH, Berlin, GermanySpherical particles of a few thousand atoms " known as nanoparticles " have been used as artificial atoms to create larger crystals that could find use in a variety of applications, such as nanoparticle-based transistors or wave guides for use in biosensors, or as computer components.
Nanoparticles are often coated with rod-like molecules to prevent further growth or agglomeration. This 'ligand shell' can be made to react with other molecules and link up with other nanoparticles to form polymers, but it does so with no particular preference the resulting structures tend to be amorphous. Nanoparticles would be even more useful if researchers could get them to assemble in a directed manner.
Francesco Stellacci and his colleagues at the Massachusetts Institute of Technology team synthesized gold nanoparticles and used a combination of 1-nonanethiol and 4-methylbenzenethiol as the ligand surface. They then used a two phase polymerization reaction inspired by the procedure to synthesize nylon. The nanoparticles were first exposed to a solution of 11-mercaptoundecanoic acid to form disulfide bonds with the 1-nonanethiol, leaving the carboxylic acid group from 1-nonanethiol protruding into space. They predicted that the polar 1-nonanethiol residues would be the first to react with the 11-mercaptoundecanoic acid, so that when the reaction was quenched it would yield nanoparticles with two modified poles. They then treated the mixture with a 1,6-diaminohexane and an activating agent to form amide bonds that would link the resulting carboxylic acid residue to the carboxylic acid residue hanging off of another nanoparticle.
Transmission electron microscopy images of the resulting precipitate revealed linear nanoparticle chains and no sign of aggregates. The particles formed films as large as 1 cm2 and up to 60 microns thick. Such films have the potential to be used as nano-waveguides for use in biosensors. Linked nanoparticles transfer light in a characteristic way, and this can be altered when they are bound to a biological molecule. This change can be used to sense the molecule's presence.
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