The National Postal Museum (NPM) houses a laboratory with a unique combination of equipment for the analytical or forensic study of philatelic materials. Analytical philately is the study of the materials that make up the objects (papers, inks, pigments, gums, etc.) through the use of scientific and engineering tools, such as elemental and molecular analysis, microscopy and different light wavelengths, or through mathematical and statistical study. Such techniques go beyond what the human senses can register and allow characteristics and components of philatelic materials to be found, identified and examined. Such characteristics and components include a wide range of things from watermarks to plate flaws, and from color differences to the molecular breakdown of paper.
The NPM lab holds the following machines, all of which work best with Windows operating systems and all of which offer non-destructive testing methods of philatelic materials.
Foster and Freeman VSC6000 with a Leica M205C Microscope (magnification range from 78x to 1600x)
The Video Spectral Comparator (VSC) uses a variety of light sources and filters to image materials in the ultraviolet, visible and infrared wavelength ranges. In combination with a high-resolution color camera, researchers can examine, compare and photograph minute details on a variety of materials. Researchers can measure objects, pinpoint particular spots for study, locate flaws and alterations, study watermarks and other security devices, and overlay images for comparison. This instrument is frequently used for the study of color, which is defined by how light interacts with material. Materials reflect and absorb light at a particular wavelengths depending on the optical properties of that material. The VSC also includes a spectrometer, capable of creating and storing spectra (visual representations of energy/wavelengths of radiation or particles emitted by a substance), and providing color values and chromaticity (color) charts.
Bruker Tracer III-SD
This handheld X-Ray Fluorescence (XRF) machine identifies elements and their relative intensity when the x-ray knocks electrons loose from their shells in an atom which releases photons. The energy or wavelength released is unique to a particular element. The XRF counts the photons and reports the related energy as peaks in a spectrum allowing the researcher to identify the elements in the object. As with the VSC, spectra can then be compared and graphed. So, for example, the elemental composition of inks and pigments can be determined, and the differences in color exposed by the VSC6000 can be explained at the atomic level.
Bruker Alpha FTIR
NPM’s Fourier-transform infrared (FTIR) spectrometer uses infrared light to gather data about the structure of molecules by reading the molecule-specific vibrations that result when the molecules absorb radiation. This machine can be used for the study both of inorganic and organic compounds. While the XRF can explain the relative levels of elements in an object, it cannot explain how the elements are distributed within compounds. So, while several different objects may register similar levels of iron, each may contain radically different compounds that are represented by different colors.
Testing Machines Inc. Precision Micrometer
The Testing Machines Inc. precision micrometer has a measuring range of 0.000-1.250 mm with a resolution of 0.1 µm. It is used to measure the thickness of sheet materials up to 1.25 mm thick and allows for data to be exported into Excel.
Researchers and scholars writing in the fields of philately and postal history are welcome to use the laboratory for the study of philatelic materials. NPM staff will provide basic training and oversight on the machines but will not analyze research results. To make an appointment to use the laboratory, please contact the Blount Research Chair at: NPMResearchChair@si.edu.