Preliminary Cleaning Approach with Alginate and Konjac Glucomannan Polysaccharide Gel for the Surfaces of East Asian and Western String Musical Instruments

Abstract

The cleaning of string musical instruments is challenging due to the traditional finishing treatments used by the makers. Multilayered coating systems were applied to Western musical instruments, while the Nakdong technique was applied in East Asia. Furthermore, by restorations and performance, dust and grime were overlapped together with polishes, adhesives, and varnishes. Gel cleaning is important in the field of conservation because of the ability to selectively remove chemical and biological degradation products from the surface, minimizing the interactions with the inner layers. In this study, hydrogels based on sodium alginate (SA) and konjac glucomannan (KG) polysaccharides were applied on laboratory mock-ups of East Asian and Western instruments to test their ability to remove synthetic soiling and sweat from the surface. In particular, SA cross-linked with calcium cations and KG cross-linked with borate gels were used. To control the exposure of the cleaning solvent on the surface of mock-ups, the moisture content of the gels was determined. The effectiveness of removing synthetic contaminants was investigated by noninvasive analytical methods. Stereomicroscopy and colorimetry, together with Fourier Transform Infrared (FTIR) spectroscopy in reflection mode and X-Ray Fluorescence (XRF), were used to evaluate the cleaning efficacy. Overall, polysaccharide hydrogels resulted in promising cleaning systems on both smooth and rough surfaces of wood.

Keywords: gel cleaning; hydrogel; konjac glucomannan; noninvasive analysis; sodium alginate; string musical instruments.

Figure 1

Chemical structure of (a) sodium alginate and (b) konjac glucomannan.

Figure 2

Schematic reconstruction of wooden mock-ups representative of (a) Western and (b) East Asian musical instrument finishing treatments.

Figure 3

Images related to the application of (a) SA gel on the sweat-Western Mock-ups (WM) surface and (b) KG gel on the soiled-WM surface; (c) surface of KG gel after cleaning the soiled-East Asian Mock-ups (EAM).

Figure 4

Stereomicroscopy images in visible and UV light of soiled-WM cleaned at different application times with SA and KG gels: (a,b) SA_1, (c,d) SA_3, (e,f) KG_1, and (g,h) KG_3.

Figure 5

Stereomicroscopy images in visible and UV light of soiled-EAM cleaned at different application times with SA and KG gels: (a,b) SA_1, (c,d) SA_3, (e,f) KG_1, and (g,h) KG_3.

Figure 6

Scatter plots showing (a) L^* and b^* values measured on WM, soiled-WM, and areas repeatedly cleaned with SA and KG gels and (b) L^* and a^* values measured on EAM, soiled-EAM, and areas repeatedly cleaned with SA and KG gels.

Figure 7

Normalized counts of Ca, Si, K, and Fe detected on (a) WM and (b) EAM. Different bars correspond to clean mock-ups (WM and EAM); to soiled mock-ups (soiled-WM and soiled-EAM); and to the soiled mock-ups after 1, 2, and 3 applications of SA (SA_1, SA_2, SA_3) and KG gels (KG_1, KG_2, KG_3). XRF values correspond to the net area counts of the Kα peak of each element normalized to time and to the average of the entire dataset of net area counts of the Rh-Kα peak with the related standard deviation.

Figure 8

XRF maps of (a) Ca (Kα) and (b) Si (Kα) on the soiled-EAM after cleaning trials with KG gel (KG_1, KG_2, KG_3, respectively from left to right); XRF map of Cl (Kα) on the sweat-EAM after cleaning trials with (c) SA and (d) KG gels at different application times (SA_1, SA_2, SA_3, KG_1, KG_2, KG_3, respectively from left to right).

Figure 9

Reflection Fourier Transform Infrared (FTIR) spectra in pseudo-absorbance acquired on soiled-EAM (black), area cleaned with SA_3 (green) and KG_3 (orange) gels, a reference of EAM without soiling mixture (gray). The marker bands selected for identifying soiling mixture and synthetic sweat components are reported.

Figure 10

Reflection FTIR spectra in (a) pseudo-absorbance and (b) after Kramers-Kronig transform of WM (gray) and sweat-WM (blue) cleaned with SA_3 (green) and KG_3 (orange). The marker bands selected for identifying soiling mixture and synthetic sweat components are reported.