CHEMISTRY 155 -
Fall 2002, Fall 2003, Spring 2004, Fall 2004, Spring 2010 (this page)
The scanning electron microscope (SEM)
equipped with x-ray energy dispersive spectrometry (XEDS) is an
important tool that can provide information about the fine structure of
surfaces as well as the
chemical composition of
archaeological materials. Studying the elemental
composition of such materials aids the archaeologist in pinpointing the age and
source (geographic region) of a specimen.
The following images
were collected from ancient pottery samples.
Secondary Electron image and Backscattered Electron image of Ancient Pottery:
The SE image (left) shows features with bright edges, but their polished, flat surfaces overall have little variation in brightness. Voids appear dark. The larger features appear embedded in a matrix comprised of tiny crushed particulates. The BSE image (right) is not sensitive to the features' edges but it is sensitive to relative atomic #. Varying shades of gray range from very bright (high atomic #) to dark (low atomic #). Voids are very dark since no electrons can escape.
Xray Energy Dispersive Spectroscopy (XEDS) of Ancient Pottery.
(left) The large particle is SiO2 (quartz, or sand).
(middle) Very bright particles are primarily CaCO3 and FeSiO3.
(right) The matrix is a conglomerate of mostly Si, Ca, Al, Fe and Ti.