Nicole C. Little

Multiple Dendrochronological Signals Indicate The Eruption Of Parícutin Volcano, Michoacán, Mexico

Abstract The eruption of Parícutin (1943–1952), a cinder cone volcano in Michoacán, Mexico, caused dendrochronological and dendrochemical responses that might be useful as general dating tools for eruptions. For the eruption period, pines near Parícutin have slightly suppressed ring widths plus high inter-annual variability of width. Wood anatomy changes include traumatic resin ducts and thin bands of false latewood. Dendrochemistry of tree rings shows little temporal variation in most elements, but beginning in 1943 sulfur content increased in rings of four trees and phosphorus content increased in rings of two trees. Hypotheses for increased S and P include new availability of pre-existing soil S and P and/or new input of S and P from the tephra itself. Pines at Parícutin also show suppressed ring widths for five years beginning in 1970, and had the eruption date not been known, the most likely conclusion from ring-width data alone would have been an eruption from 1970 to 1974. However, the 1970s suppression was in response to defoliation by a pine sawfly outbreak, not an eruption. For dendrochronological dating of cinder-cone eruptions, a combination of multiple characteristics (width, chemistry, and anatomy) would be more reliable than depending on any one characteristic alone.

Degradation of ‘Lumarith’ Cellulose Acetate

Abstract Objects manufactured from cellulose acetate comprise one of the most problematic groups of plastic in the collections of the Smithsonian Institutions National Museum of American History (NMAH). To understand better cellulose acetate degradation, a ‘salesmans sample kit’ of ‘Lumarith’ brand, injection-molded, cellulose acetate color samples, manufactured by the Celluloid Company in the early twentieth century and now in the NMAH collection, was studied using minimally invasive analytical techniques at the Smithsonian Institutions Museum Conservation Institute (MCI). The kit includes 49 plastic coupons that vary in color, transparency, chemical composition and current state of degradation. Results of analysis were compared with Celluloid Company records at the NMAH Archives Center and Celanese Corporation in Narrows, Virginia, in order to determine the causes for their current level of preservation or degradation. The possible reasons for the degradation of some coupons are discussed; methods are proposed for identifying cellulose acetate objects that are at risk and for early detection of degradation.

Manganese in Black Crusts on Seneca Sandstone

Introduction: Scattered black deposits are found on surfaces of the Smithsonian Castle (1849-1855) and Enid Haupt Garden Gateposts (1987), as seen in Figures 1A. The structures are made of Seneca sandstone, an arkosic micaceous sandstone quarried near Washington, DC. Photographs document that deposits have increased on the relatively new gateposts over the last six years. Generally, black deposits on sandstone are attributed to solubilized silica that incorporates dark particulate material [1]. XRF analysis of a sample taken from a gatepost (Fig. 1B) and in situ analysis of deposits on the Castle instead indicate that the deposits are manganese rich, likely colored by small amounts of manganese oxide. The deposits are thus comparable to desert varnishes on sandstone, which contain mineralized manganese and sometimes iron as a result microbial action [2, 3]. Normally soiling on buildings is associated with moisture and rainwater patterns, and the seemingly random locations of the manganese-rich deposits without a clear relationship to water remain a puzzle. Manganese-rich black deposits have not been reported on other sandstone buildings in temperate climates; it is not clear to what extent they are present elsewhere and may have been incorrectly identified. Correct characterization of such deposits is important from a conservation standpoint in order to determine the most effective method of removal, if required.

Cleaning Marble with Ammonium Citrate

Abstract Ammonium citrate solutions were tested to determine possible damage on marble using two concentrations, four different values of pH and several variations in application. As pH dropped from values of 10 to 7, marble chips immersed in the solutions showed increasing dissolution of calcite, and polished marble tiles to which solutions had been applied showed increasing loss of gloss and brightness. The least damage to marble tiles was produced when solutions were covered during application, and single cleanings were found to be less damaging than multiple cleanings of the same total application time. Comparison with other cleaning agents – ammonium thioglycolate and ethylenediaminetetraacetic acid (EDTA) – showed that ammonium citrate solutions could be as mild as thioglycolate when used in some conditions, such as high pH and low concentration. In contrast, ammonium citrate solutions could harm the stone significantly when used in other conditions, such as pH 7 or high airflow. In these cases, the damage was nearly as much as a 2% solution of EDTA at pH 10. This study emphasizes the need to develop new cleaning products, research which can only go hand in hand with a better understanding of the various interactions taking place between cleaning agent, substrate and environment.