manuscript lab


FEI ESEM XL30 (environmental scanning electron microscopy)

The electron scanning microscope has a large sample chamber (D ~ 28,5 cm) and adjustable pressure (below 10-5 Pa and up to 103 Pa for high and low vacuum modes, respectively. In the high vacuum mode and at 30kV accelerating voltage, its resolution reaches 3.5 nm. For cultural heritage applications, one usually works in the environmental mode, i.e., under low vacuum conditions using water vapor and now specific sample preparation. The microscope is equipped with a number of detectors for a suitable imaging of the surfaces in addition to an energy-dispersed x-ray analyzer to determine the elemental composition.

Fig. 1: ESEM XL30, BAM

Olympus BX51 (light microscopy)

This is a classic microscope for studies of biological samples. The setup features lenses for 50, 100, 200 and 500 times magnification and facilities to perform fluorescence, polarization, and dark and bright field microscopy. For image recording, a digital camera with a resolution of 2080 x 1544 pixels is connected to computer. The microscope is perfectly suited for fiber analysis.

Fig. 2: Olympus BX51

Keyence VHX-5000 (3D-Microscopy)

An all-purpose microscope features digital focusing technology to obtain high-resolution in-depth images. A high-speed stage with mounted lenses for 20 to 200 times magnification is connected to the computer unit that covers observation, image capture, and measurement. The microscope is mostly used to analyze surface topography.

Fig.3: Keyence VHX-5000

DinoLite (UV / VIS / NIR microscopy)

The Dino Lite digital stereomicroscope (Fig. 4) features built-in LED illumination at 395 nm and 940 nm and a customized external white light source. During use, the microscope is fastened to a small tripod or mounted on a Plexiglas ring holder that incorporates a white light source.

Fig. 4: DinoLite AD413T-I2V

Eureka Vision (Multispectral imaging)

With the Eureka Vision system, LED light sources provide narrowband illumination from the UV (365 nm) through the visible spectrum to the near-IR (1040 nm) (Fig. 5). LED illumination offers several advantages. It does not expose vulnerable originals to heat, it minimizes the light exposure necessary for multi-spectral imaging, and it supports pixel-for-pixel registration of images captured with high-resolution cameras. The system features a 50 mp monochrome camera and a specialized 120mm quartz lens that achieves sharp focus (is apochromatic) at all 13 wavelengths of illumination. A dual filter wheel in front of the lens enables the capture of images of UV reflectance and of different colors of UV fluorescence. Raking lights in blue and IR provide low-incidence angle illumination to discern the topography and fine surface texture of parchment, papyrus or paper originals.

Fig. 5: Multispectral camera system

SpectroEye, Gretag-Imaging AG (Visible Spectrophotometry)

The investigations of the colorants are performed with the color spectrometer SPM 100 (Gretag-Imaging AG, Regensdorf, Switzerland, Fig. 6), which measures the reflection of visible light (from 380 to 730 nm) and has a measurement spot of 3 mm diameter. The probe moves over the surface of the sample, which is illuminated for half a second, using a small 2 W bulb. The characteristic reflectance spectrum is then measured and stored. By comparing this specific spectrum with a database, it is possible to identify most of the colorants—organic as well as inorganic materials.

Fig. 6: Spectral Photometer SPM 100 ()Gretag Imaging AG)

XRF spectrometers (X-ray fluorescence analysis)

The simplest X-ray fluorescence spectrometer is a handheld XRF spectrometer TRACER III-SD (Bruker Nano GmbH, Fig. 3) with an interaction spot of ca. 1 cm. All measurements are conducted with a low-power rhodium tube; excitation parameters are, respectively, 15 kV and 55 µA to determine light elements and 40 kV and 15µA to detect heavy elements. The 3-kg instrument would be the first choice when a “quick and dirty” identification of elements is required. Since the instrument is operated with batteries, it can be taken on any field trip.

Two µ-XRF scanners use an air-cooled low-power X-ray tube, poly-capillary X-ray optics, and an electrothermally cooled X-flash detector. The silicon drift detector, with high-speed, low-noise electronics, permits an energy resolution of 160 eV for Mn–Ka radiation at a count rate of 10 kcps. It has an active area of 5 mm2 and an 8 µm thick Dura-beryllium window. The geometry between the primary beam, the sample, and the detector is fixed at 0°/40° relative to the perpendicular of the sample surface.

The first one, ArtTAX (Bruker Nano GmbH, Fig. 4), is well known in the field of cultural heritage and is standard equipment in the majority of large museums. It has a measuring spot size of 70 µm diameter, a CCD camera for sample positioning, and an electrothermally cooled Xflash detector (SDD, area: 30 mm2) with an energy resolution of <150 eV at 10 kcps. The movable probe is oper-ated by XYZ motors that allow for spot measurements as well as line and small area scans. Open helium purging in the excitation and detection paths allows for detection of light elements (Z = 11). Measurements are made using a 30W low-power Mo tube, operating at 50 kV and 600 µA, with an acquisition time of 10-100 s (live time). The mobile XRF probe moves over the object at a distance of 5 mm and stops for the duration of a single measurement. The areas of investigation are usually determined beforehand. This instrument is used for a quantitative analysis of iron gall inks, pigments, etc.

The imaging spectrometer, Jet Stream (M6, Bruker Nano GmbH, Fig. 5), has a variable measuring spot size (75–850 µm diameter) , two microscopes for sample positioning and for mapping the large areas, and an electrothermally cooled Xflash detector (SDD, area: 30 mm2) with an energy reso-lution of <150 eV at 10 kcps. Its movable probe is mounted on a large frame, allowing for the mapping of surfaces up to 60 x 80 cm. Unlike the Artax, the measurement is performed “on the fly“, i.e., while the probe is moving. Typically, the measurements are made using a 30W low-power Rh tube, operating at 50 kV and 600 µA, with an acquisition time of 2-150 ms (live time). We use this instrument to produce elemental maps of paintings, drawings, and manuscripts.

Fig. 7: TRACER III-SD (Bruker Nano GmbH)

Fig. 8: ARTAX (Bruker Nano GmbH)

Fig. 9: Jet Stream M6 (Bruker Nano GmbH)

ExoScan 4100 Agilent (FTIR spectroscopy)

For FTIR spectroscopy, a method used over the last 80 years, samples were usually measured in transition mode, which means that small samples had to be taken from an object. Recently, non-destructive methods have been developed to study the surfaces of different objects. The miniaturization of IR sources and detectors has enabled the development of a new generation of portable spectrometers that allow handheld investigation in a diffuse reflection mode (e.g., A2 Technologies). We use the ExoScan to analyze organic material (Fig. 10a). During the measurement, it is also possible to fix the spectrometer on a tripod (Fig. 10b).

Fig. 10a: ExoScan 4100 (Polytec GmbH), measurement in diffuse reflection.

Fig. 10b: ExoScan 4100 with tripod, measurement in diffuse reflection.

Raman spectrometer Renishaw in Via (Raman spectroscopy)

The In Via Raman spectrometer (Renishaw, Fig. 8) has been specially adapted for the study of objects in the Cultural Heritage field. Instead of a microscope, it is equipped with two fiber optics probes connected to lasers operating at 530 and 785 nm, respectively. The probes are connected to a camera to position the object and a CCD camera for signal registration. Measurements are typically carried out with a x50 lens and an output power of 5-10 mW in the spectral range 100-3600 cm-1 with a spectral resolution of 4 cm-1. 300 scans are co-added per spectrum collected with 20 s exposure.

Fig. 11: In Via Raman spectrometer (Renishaw GmbH)

Artec Eva and Space Spider 3D-Scanners

Fig. 12: Artec hand-held 3D Scanners

Keyence VR 3200 3D Profilometer

Fig. 13: 3D Profilometer and measurement of a cuneiform tablet