SHORT COMMUNICATION: MICRO-RAMAN IDENTIFICATION OF BLOOM FORMED ON A HISTORICAL PRINT ARTIFACT
VINCENT OTIENO-ALEGO, JENNIFER HODGEMAN, & DUDLEY C. CREAGH
2.1 ABOUT THE ARTIFACT
The artifact, which is approximately 65 x 103 cm2 in size, has been hanging in a general manager's office for about seven years. It is framed under glass with an ornamental wooden frame, on a linen backing adhered to a laminated board. The picture itself is centered in the upper portion of the print, giving room below for the decorative printed text ADELAIDE (see fig. 1). A note attached to the frame indicates that previous conservation treatment was performed in 1972.
2.2 EXPERIMENTAL DETAILS
The powdery deposits on the print were brushed off into a sealable polyethylene bag. Preliminary examination using an ordinary light microscope showed the solid deposit to be a mixture of a number of microsized crystals. A sample of this powder (approximately 1 mg) was placed on a microscope slide for direct Raman microanalysis.
Raman spectra were recorded using a Raman imaging microscope (Renishaw PLC, model 2000) coupled with an Olympus BH2 microscope. The Ramascope is equipped with an air-cooled charge-coupled device (CCD) detector, a motorized XYZ stage, and an image-viewing video camera. A near infrared laser source emitting at 780 µm was used as the excitation source. The Ramascope was set up in its confocal mode (Williams et al. 1994) for maximum spatial resolution (approximately 0.7 µm). With this setting, individual solids within the mixture were separately identified. A representative sample area of 1200 x 1200 µm2 was defined with the aid of the motorized stage. The individual particles enclosed in this area were each pinpointed using the video viewer, and the targeted solid was analyzed by focusing the laser beam via the 50x microscope objective. Integration times ranged between 20 and 40 seconds, with 5 to 10 spectral accumulations.
Attempts to physically separate the individual particles for complementary analysis using infrared microscopy were unsuccessful because of the inability to focus the IR beam into a sufficiently small area.