JAIC 2001, Volume 40, Number 1, Article 3 (pp. 35 to 41)
JAIC online
Journal of the American Institute for Conservation
JAIC 2001, Volume 40, Number 1, Article 3 (pp. 35 to 41)

SHORT COMMUNICATION: MICRO-RAMAN IDENTIFICATION OF BLOOM FORMED ON A HISTORICAL PRINT ARTIFACT

VINCENT OTIENO-ALEGO, JENNIFER HODGEMAN, & DUDLEY C. CREAGH



3 RESULTS AND DISCUSSION

Figure 2 shows a typical white light micrograph of the powdery deposit examined under a light microscope using a 10x microscope objective. This examination revealed three distinct types of crystalline material. The deposit included relatively large transparent crystals (see example labeled A in fig. 2) dispersed amid the bulk of much smaller, more rounded white crystals (example labeled B, fig. 2) and a few orange-colored crystals (example labeled C). Some black particles (labeled D) were also observed, as well as white fiberlike materials (labeled E) whose lengths ranged between 50 and 200 m. These particles hereafter will be referred to simply as solids A, B, C, D, and E, respectively.

Raman microanalysis of all the solid particles enclosed in the predefined area of 1200 x 1200 m2 was undertaken by focusing the laser onto the individual particles via the microscope objective. Identification of these solids was made, in each case, by comparison of their Raman spectra with reference spectra on the inhouse database, which is continuously updated with any known data. This reference library consists mainly of spectra present in the commercial Nicolet spectral database as well as additional in-house spectra recorded over time from analytical grade reagents. Typical Raman spectra obtained for the different solids, together with the reference spectra used for their identification, are presented in figure 3. The spectra of the predominant solid B matched closely that of reference calcium carbonate (CaCO3) (fig. 3a).The spectra from solid A were in perfect agreement with the reference spectrum of paratoluenesulfonamide (CH3C6H4SO2NH2) (fig. 3b). Solids C, D, and E were also unambiguously identified to be quartz (fig. 3c), black carbon (fig. 3d), and cellulose (possibly fiber from the paper matrix) (fig. 3e), respectively.

Fig. 3. Representative Raman spectra recorded for the different solids (spectra labeled S) together with the reference spectra (labeled R) used for their identification: (a) solid B was identified as CaCO3; (b) solid A was identified as paratoluenesulfonamide; (c) solid C was identified as quartz; (d) solid D was identified as black carbon; (e) fiberlike material E was identified as cellulose.

The occurrence of paratoluenesulfonamide may be linked to the use of chloramine-T (the sodium derivative of N-chloro-p-toluenesulfonamide: ([CH3C6H4SO2N(Cl)Na]), which was a popular paper bleaching reagent in the 1960s and 1970s (Lienardy and Van Damme 1990).When dissolved in ethanolic solution, chloramine-T slowly hydrolyzes, releasing hypochlorite ions (Corrigan 1997) according to the following equation:

Thus, the bleaching action of chloramine-T is comparable to that of sodium hypochlorite, except that in this case the bleaching process is much slower and therefore more controllable. The Cl-free toluenesulfonamide identified in this study is a product of this cleavage reaction.

Chloramine-T bleaching was considered to be simple, efficient, safe, and less harmful to the paper (Hey 1977). Paper treated with chloramine-T required only a simple rinse because traces of the chemical were presumed to have a bactericidal action long after the treatment (Lienardy and Van Damme 1990). The occurrence of its residues on this print artifact is thus not surprising. The idea that chloramine-T is safe has since been amended. Chloramine compounds are unstable, and the residual chemicals present on paper progressively hydrolyze well after the treatment time, resulting in the formation of detrimental acidic species such as hypochlorous acid and hydrochloric acid. These acids can lead to the breakdown of cellulose through acid-catalyzed hydrolysis (Hey 1977). Another disadvantage linked with the use of chloramine-T is its strong bonding to cellulose, which makes it very difficult to wash it off with water alone. Thus, after bleaching with chloramine-T, the paper is normally rinsed in dilute acetic acid (to break down any residual chloramine-T), then washed with water to remove excess acid and any water-soluble precipitates, followed by a rinsing in ethanol solution to remove organic-type particulates that are less soluble in water (Hey 1977). Finally, the bleached paper is deacidified in calcium hydroxide (Ca[OH]2) solution, which on long exposure to air would allow the formation of the CaCO3 as observed.

The black carbon particles most likely came from the print ink, while the cellulose fibers broke loose from the aging paper. The source of the few quartz crystals identified in the white solid deposit is probably trapped dust/sand particles from the environment.


Copyright 2001 American Institution for Conservation of Historic & Artistic Works