Detailed Tour of Labs

Semi-automatic grinder and polisher & Vibratory polisher (Buehler)

These machines aid in the preparation of samples that are to be examined with reflected light microscopy. The polisher/grinder essentially does what you do by hand when you polish embedded cross sections from painted surfaces.

Samples removed from metal, ceramic or glass artifacts are first embedded “face down” by casting an epoxy resin into a cylindrical mold. The cylinder is then fitted onto the polisher/grinder and the surface of the cylinder is ground and polished using a variety of abrasives. Final polishing is achieved with the vibratory polisher using very fine silica or alumina particles.

The polished face of the samples can be examined using reflected light microscopy to reveal their microstructure. Polished metal cross sections are often etched prior to examination in order to better reveal features of their microstructures.

Gas chromatograph (GC) (Hewlett Packard)

Gas chromatography is a column separation technique. In principle, it resembles the liquid column chromatography some students encounter in their organic chemistry laboratory course. In lab, you might have used a glass column packed with silica gel and used that to separate compounds dissolved in a liquid with which you eluted the column.

This instrument separates mixtures of compounds in the gaseous phase based on their relative affinities for the stationary phase inside a long, slender column. Compounds have to be volatilized from solution before they enter the column, which is in a heated compartment. Components are identified based on comparison of their retention time—essentially the time they spend in the column—with that of reference materials.

Gas chromatography can be used to identify resins, different types of binding media, polymers, etc. Polymer identification is typically accomplished by first pyrolyzing the polymer (we have a CDS Pyroprobe pyrolysis accessory): the polymer sample is heated to decompose it into smaller, more volatile components.

High-performance liquid chromatograph (HPLC)

This instrument consists of many components that are linked together by tubes that can withstand high liquid pressure.

Like gas chromatography, high-performance liquid chromatography is a column separation technique. However, HPLC separates components in the liquid phase and separation occurs close to room temperature.

Our HPLC system has four different types of detectors that signal the arrival of components at the end of the column. Each different detector works based on a different principle(UV or visible absorption, refractive index, fluorescence), which will allow us to chose the most appropriate one for a particular separation protocol.

HPLC is widely used in the identification of natural dyes. Special columns permit the separation of mixtures of very large molecules (including polymers), such as cellulose, based on the size of the molecule.

Reflected light & fluorescence microscope (Leica)

This microscope is very useful for studying embedded and polished cross sections using reflected visible light and ultraviolet light induced visible fluorescence. Many organic substances fluoresce with characteristic color when illuminated with UV light. Fluorescent dyes are often used to distinguish between different types of organic compounds (lipids, resins, proteins, starches): these dyes selectively stain certain types of organic compounds.

Reflected light microscope (Zeiss)

This microscope is used primarily for studying polished cross sections from metal and ceramic artifacts.

Polarized light microscopes (Nikon and Olympus)

Polarized light microscopy is an indispensable tool for conservators in identifying pigments, fibers, woods, etc. PLM is often combined with microchemical testing.

Fourier-transform infrared spectrometer and infrared microscope (Thermo Electron, Nicolet)

Fourier-transform infrared spectroscopy is a very useful method for identifying a variety of inorganic and organic compounds based on their selective absorption of radiation in the mid-infrared region of the electromagnetic spectrum. The infrared spectrum of a sample can be matched with that of reference compounds using search-match software that accesses thousands of spectra of artists’ materials and compounds used in conservation.

FTIR is often the first step toward identifying organic materials.

Samples can be measured in IR transmission, reflection, or attenuated total reflection modes (ATR). Our FTIR spectrometer is equipped with a microscope accessory, which allows us to obtain spectra from very small samples. We also have a micro-ATR accessory for the microscope as well as a SplitPea ATR accessory for the bench compartment.

X-ray Powder Diffractometer (Philips)

X-ray powder diffraction allows the identification of crystalline compounds, such as crystalline pigments, corrosion products, minerals and stone. Each crystalline compound produces a unique diffraction pattern, which is captured on x-ray sensitive film. Diffraction patterns are read from the film after development and are matched to reference patterns using printed manuals or a search-match software.

Environmental testing chamber (Blue M)

The environmental testing chamber allows the user to expose samples to constant or cycling temperature and humidity conditions. Conditions are typically chosen in hopes of accelerating chemical and physical processes that lead to the deterioration of materials. In other words, environmental testing chambers may be used for accelerated aging of specimens.

We use the environmental testing chamber to prepare “mock-up” specimens on which students can perform treatments; to explore changes in materials under different environmental conditions; and to explore whether a particular treatment may lead to noticeable changes after an artifact undergoes further aging.

X-ray fluorescence spectrometer (XRF) (Röntec ArtTAX)

X-ray fluorescence spectroscopy is an atomic spectroscopy method that allows users to identify and quantify elements of atomic number equal to or higher than 11 (sodium, Na, has an atomic number of 11). Our instrument is designed specifically for the elemental analysis of cultural materials, as it obtains x-ray fluorescence spectra in-situ, right on the surface of the artifact. XRF is a surface analytical technique and sampling depth ranges from several micrometers to about a millimeter, depending on the x-ray tube used and the overall composition of the sample matrix.

XRF analyses are typically very rapid, a good spectrum can be collected in less than a minute in most cases! Elemental composition is helpful in identifying pigments, metals and alloys, etc. XRF, however is not very helpful for identifying organic compounds.

Elemental analyzer (EA)
(Carlo Erba)

The elemental analyzer provides quantitative analysis of the carbon, hydrogen, nitrogen, sulfur and oxygen composition of inorganic and organic substances. Samples are combusted (and some are reduced), producing nitrogen (N2), carbon dioxide (CO2), sulfur dioxide (SO2) gases and water vapor, which are then separated in a gas chromatographic column and quantified by a detector.

This analytical method is useful in studying adsorption processes as well as deterioration and aging mechanisms. The nitrogen content of paper may be used as an indicator of gelatin sizing and elemental analysis therefore can be used to study the loss of gelatin sizing in paper during aqueous conservation treatments.

Modulated Differential Scanning Calorimeter (MDSC) (TA Instruments)

MDSC subjects materials to modulated thermal temperature ramps in the range of -90 to 600 ºC while measuring heat flow into or out of the sample as a result of phase transitions or chemical reactions. Information garnered through calorimetry includes heat capacity (Cp), glass transition temperature (Tg), melting point (Mp), crystallization temperature (Tc), cure kinetics, percent polymer crystallinity, and oxidative stability.

X-ray fluorescence spectrometer (XRF) (Röntec ArtTAX)