Reiche I.,Paris-Sorbonne University |
Reiche I.,Heritage Foundation |
Muller K.,Paris-Sorbonne University |
Mysak E.,Straus Center for Conservation and Technical Studies |
Mysak E.,Yale University
Applied Physics A: Materials Science and Processing | Year: 2015
Examination of Gustave Courbet’s L’Homme blessé (Musee d’Orsay, Paris), a painting with three successive compositions on a single canvas, was undertaken with scanning electron microscopy coupled with an energy-dispersive X-ray analyzing system (SEM–EDX) on cross sections taken in the 1970s at the Laboratoire de Recherche de Musées de France, Paris and confocal X-ray fluorescence spectroscopy (CXRF) analysis adjacent to the sample locations of the three previously removed cross sections. Recent developments of in situ techniques such as CXRF have enabled investigation of the chemical composition of complicated paint layering without sampling. Here, we compare depth profiling by CXRF analysis with SEM–EDX data from cross sections with the goal of understanding how well CXRF data represent such a complicated paint stratigraphy. Beyond suggesting the paint palettes for Courbet’s three compositions, this new data provide insight into the complex paint layer stratigraphy of eight or more layers and serve as the basis for interpreting further analyses by scanning XRF and CXRF of additional areas of interest on the painting. Data from these additional locations will be discussed in a forthcoming paper. © 2015, Springer-Verlag Berlin Heidelberg.
Kroll J.H.,Massachusetts Institute of Technology |
Donahue N.M.,Carnegie Mellon University |
Jimenez J.L.,University of Colorado at Boulder |
Kessler S.H.,Massachusetts Institute of Technology |
And 14 more authors.
Nature Chemistry | Year: 2011
A detailed understanding of the sources, transformations and fates of organic species in the environment is crucial because of the central roles that they play in human health, biogeochemical cycles and the Earth's climate. However, such an understanding is hindered by the immense chemical complexity of environmental mixtures of organics; for example, atmospheric organic aerosol consists of at least thousands of individual compounds, all of which likely evolve chemically over their atmospheric lifetimes. Here, we demonstrate the utility of describing organic aerosol (and other complex organic mixtures) in terms of average carbon oxidation state, a quantity that always increases with oxidation, and is readily measured using state-of-the-art analytical techniques. Field and laboratory measurements of the average carbon oxidation state, using several such techniques, constrain the chemical properties of the organics and demonstrate that the formation and evolution of organic aerosol involves simultaneous changes to both carbon oxidation state and carbon number. © 2011 Macmillan Publishers Limited. All rights reserved.
Lopez A.R.,University of the Basque Country |
Gobantes F.B.,University of the Basque Country |
Khandekar N.,Straus Center for Conservation and Technical Studies
European Journal of Science and Theology | Year: 2015
The megalithic burial monuments are the physical evidence of the social, economical and religious evolution in the Neolithic Era. Their presence all over Europe reveals their significance. They are usually collective tombs and are always located in natural sites. For many years, particularly since the beginning of the 20th century, the megalithic heritage of the Basque Country, a region of Northern Spain bordering with the South of France, has been subjected to agricultural use, intensive reforestation and other changes that have resulted in various damage and even losses of megaliths. At present a systematic protocol is required to diagnose their condition and set effective intervention processes. The operational goals are the attainment of their legibility, perceptual recognition, physical consolidation and balance with the immediate environment. In the Basque Country and particularly in the province of Biscay, the implementation of this protocol aims to properly recover and value this heritage for its maintenance for the future. Over one third of the ca. 100 megaliths registered in Biscay have been restored. The design of new megalithic routes and promotion programmes has been essential for the public access and conservation of these archaeological sites. © 2015, Ecozone, OAIMDD.
Mysak E.R.,Lawrence Berkeley National Laboratory |
Mysak E.R.,Straus Center for Conservation and Technical Studies |
Starr D.E.,Lawrence Berkeley National Laboratory |
Starr D.E.,Straus Center for Conservation and Technical Studies |
And 3 more authors.
Review of Scientific Instruments | Year: 2010
We discuss a new approach for the measurement of the surfaces of free aerosol particles with diameters from 50 to 1000 nm. Particles in this size range have significant influence on the heterogeneous chemistry in the atmosphere and affect human health. Interfacing an aerodynamic lens to an ambient pressure x-ray photoelectron spectrometer permits measurement of the surface chemical composition of unsupported aerosol particles in real time. We discuss the basic considerations for the design of such an instrument, its current limitations and potentials for improvement. Results from a proof-of-principle experiment on silicon oxide particles with average diameters of 270 nm are shown. © 2010 American Institute of Physics.
News Article | March 21, 2016
Today, every color imaginable is at your fingertips. You can peruse paint swatches at hardware stores, flip through Pantone books, and fuss with the color finder that comes with most computer programs, until achieving the hue of your heart's desire. But rewind to a few centuries ago and finding that one specific color might have meant trekking to a single mineral deposit in remote Afghanistan—as was the case with lapis lazuli, a rock prized for its brilliant blue hue, which made it more valuable than gold in medieval times. The history of pigments goes back to prehistoric times, but much of what we know about how they relate to the art world comes from Edward Forbes, a historian and director of the Fogg Art Museum at Harvard University from 1909 to 1944. Considered the father of art conservation in the United States, Forbes traveled around the world amassing pigments in order to authenticate classical Italian paintings. Over the years, the Forbes Pigment Collection—as his collection came to be known—grew to more than 2,500 different specimens, each with its own layered backstory on its origin, production, and use. Today, the collection is used mostly for scientific analysis, providing standard pigments to compare to unknowns. Narayan Khandekar is the director of the Straus Center for Conservation and Technical Studies at the Harvard Art Museums and the collection's custodian. For the last 10 years, Khandekar has rebuilt the collection to include modern pigments to better analyze 20th century and contemporary art. A lot has changed in the art world since painters worked with "colormen"—as tradesmen in dyes and pigments were known—to obtain their medium. The commercialization of paints has transformed that process. "Artists today will use anything to get the idea that's in their head into a physical form," Khandekar says. "It could be pieces of plastic. It could be cans of food. It could be anything. We need to be able to identify lots of different materials that are industrially produced as well as things that are produced specifically for artists' use." The way he describes his work researching and cataloging pigments is akin to detective work. "We use our instruments in the same way that forensic scientists do," Khandekar says. "We examine and find out what we can about the key compounds that will tell us the material's origin." But instead of tools such as DNA analysis, he and his team of conservation scientists use techniques such as Raman spectroscopy, mass spectrometry, gas chromatography, and electron microscopy to map out the precise chemical composition of a pigment. For example, their work was instrumental in proving that a Jackson Pollock painting "rediscovered" in 2007 was actually a fake, after pigment analysis revealed that a specific red color was manufactured 20 years after the artist's death. The color, Red 254, was a by-product of a chemical reaction first documented in 1974; it's also nicknamed "Ferrari red." "Every pigment has its own story," Khandekar says. With that in mind, we asked him to share the stories of 10 of the rarest and most interesting pigments in the Forbes collection. Synthetic Ultramarine "This was discovered in 1826 as the result of a contest. In a way it is like discovering how to make gold as artists no longer had to buy natural ultramarine at great cost." Mummy Brown "People would harvest mummies from Egypt and then extract the brown resin material that was on the wrappings around the bodies and turn that into a pigment. It's a very bizarre kind of pigment, I've got to say, but it was very popular in the 18th and 19th centuries." Brazilwood "Brazilwood is any of several tropical trees of the senna genus. Its hard, red-color wood has had limited use for violins, bows, veneer, and high-quality furniture. The wood contains the colorant brasilin, which gives a deep-red to brownish color. Brazilwood dye has been used for textile and leather dyes, inks, paints, varnish tints, and wood stains." Quercitron "A yellow vegetable dye, quercitron is extracted from the black or dark brown bark of the black oak, Quercus velutina, that is native to the Eastern and Midwestern parts of the United States." Annatto "The lipstick plant—a small tree, Bixa orellana, native to Central and South America—produces annatto, a natural orange dye. Seeds from the plant are contained in a pod surrounded with a bright red pulp. Currently, annatto is used to color butter, cheese, and cosmetics." Lapis Lazuli "People would mine it in Afghanistan, ship it across Europe, and it was more expensive that gold so it would have its own budget line on a commission." Dragon's Blood "It has a great name, but it's not from dragons. [The bright red pigment] is from the rattan palm." Cochineal "This red dye comes from squashed beetles, and it's used in cosmetics and food." Cadmium Yellow "Cadmium yellow was introduced in the mid 19th century. It's a bright yellow that many impressionists used. Cadmium is a heavy metal, very toxic. In the early 20th century, cadmium red was introduced. You find these pigments used in industrial processes. Up until the 1970s, Lego bricks had cadmium pigment in them." Emerald Green "This is made from copper acetoarsenite. We had a Van Gogh with a bright green background that was identified as emerald green. Pigments used for artists' purposes can find their way into use in other areas as well. Emerald green was used as an insecticide, and you often see it on older wood that would be put into the ground, like railroad ties."
Verborg M.,Straus Center for Conservation and Technical Studies
Restaurator | Year: 2012
The paper describes the effects of light bleaching with metal halide lamps on selected chemical and mechanical properties of six different naturally aged 18th-21st century papers. Treatments included: pre-washing under ambient light, prolonged immersion in a dilute calcium hydroxide solution while kept in the dark, exposure to high-intensity light in dry condition, and immersion in a dilute calcium hydroxide solution while exposed to high-intensity light (light bleaching treatment). The effects of the treatments on the papers were evaluated by the Yellowness Index (YI), pH, tensile strength (0-span tensile test) and the degree of polymerization. All these measurements and tests were repeated after artificial thermal ageing to evaluate the treatment effects over the long term. Light bleaching proved effective in reducing the yellowing in the rag paper after treatment and after ageing, although some colour reversion was observed after ageing. Light bleaching treatment brightened the chemical woodpulp paper, but the effect was nullified after ageing due to a high degree of colour reversion. Light bleaching showed only limited brightening effects on woodpulp paper after treatment; woodpulp paper samples darkened more during ageing than the rag paper and chemical woodpulp paper. Immersion in the alkaline bath increased the pH of all papers tested in this study and exposure to light in dry condition turned out to be detrimental for the pH both after exposure and after ageing. Exposure to light in dry condition and aqueous light bleaching both caused a decrease in the tensile strength of paper samples in the short-term. Light bleaching treatment caused a decrease in the degree of polymerisation of cellulose after treatment and after ageing. © De Gruyter Saur 2012.