Materials Engineering of Violin Soundboards by Stradivari and Guarneri

Abstract

We investigated the material properties of Cremonese soundboards using a wide range of spectroscopic, microscopic, and chemical techniques. We found similar types of spruce in Cremonese soundboards as in modern instruments, but Cremonese spruces exhibit unnatural elemental compositions and oxidation patterns that suggest artificial manipulation. Combining analytical data and historical information, we may deduce the minerals being added and their potential functions-borax and metal sulfates for fungal suppression, table salt for moisture control, alum for molecular crosslinking, and potash or quicklime for alkaline treatment. The overall purpose may have been wood preservation or acoustic tuning. Hemicellulose fragmentation and altered cellulose nanostructures are observed in heavily treated Stradivari specimens, which show diminished second-harmonic generation signals. Guarneri's practice of crosslinking wood fibers via aluminum coordination may also affect mechanical and acoustic properties. Our data suggest that old masters undertook materials engineering experiments to produce soundboards with unique properties.

Keywords: ICP-MS; IR spectroscopy; NMR spectroscopy; X-ray absorption spectroscopy; cultural heritage.

Figure 1

Optical‐sectioning hyperspectral images of spruces: a) Amati SC1, b) Stradivari SC4, c) modern SM3, and d) modern SM5, showing tracheid cells with bordered pits (arrows). e) The broader autofluorescence peaks of Amati and Stradivari suggest chemical heterogeneity due to lignin oxidation.

Figure 2

a) XRD patterns of Stradivari's spruce (SC4), with the arrow labeling the (004) peak. b) The (004) peaks of Cremonese, old, and modern spruces. Old building samples SO1 and SO3 exhibit weaker peaks, suggesting reduced crystallite length.

Figure 3

a) ¹³C{¹H} multiCP ssNMR spectra of Cremonese spruces, compared to the average of modern spruce controls (SM1–SM5). HC: hemicellulose. TC/AC/CC: total/amorphous/crystalline cellulose. b) Infrared absorption spectra of Cremonese spruces.

Figure 4

Elemental profiles of Cremonese spruces and maples measured by ICP‐MS, compared to modern and age‐matched controls, represented by multi‐dimensional scaling analysis.

Figure 5

SHG images of a) modern, b) Amati, and c) Stradivari spruce sample. The visible structures include tracheid cell walls (star), bordered pits (dashed circle), and middle lamella (arrowhead). Scale bar=10 μm. Straight lines in (c) are camera detector artifacts that become visible after image enhancement. d) SHG intensities of different regions in different samples, with error bars representing the standard deviation.

Figure 6

a) Brightfield microscope image of Guarneri spruce (SC6). The red box is analyzed for XRF. b) Cumulative XRF spectra with curve fitting for different elements. c) Spatial mapping of individual elements by XRF. d) XANES spectra of Guarneri spruce compared to standards. e) ²⁷Al ssNMR spectra of Guarneri and Stradivari spruces.