A multidisciplinary materials characterization of a Joannes Marcus viol (16thcentury)
- Letizia Bonizzoni†1Email author,
- Claudio Canevari†2,
- Anna Galli†3, 4,
- Marco Gargano†1,
- Nicola Ludwig†1,
- Marco Malagodi†5 and
- Tommaso Rovetta†5
© Bonizzoni et al.; licensee Chemistry Central Ltd. 2014
Received: 19 February 2014
Accepted: 18 June 2014
Published: 3 July 2014
Several musical instruments in the past centuries were decorated with engravings, inlays, or paintings. This paper focuses on an integrated approach to detect and characterize the kind of dyes when used for the decorations. The multi analytical campaign was performed on a viol made by Joannes Marcus in the second half of the 16th century. The instrument has been shattered during World War II, and the fragments are now held in Conservatorio Giuseppe Verdi in Milan; they still conserve the original black and white purflings and the painted decorations. The study is of critical importance since Joannes Marcus worked in the sixteenth century and, in this very period, some executive features were introduced in musical instrument making, which are now veritable standards for this kind of instruments.
At first, UV fluorescence examination and reflectographic analysis have been performed on the different fragments in order to characterize, respectively, the distribution of varnishes and glues on the surface and to select the areas treated with metal-gall inks that result transparent by long wave IR reflectographic technique. The materials were therefore characterized with X-Ray Fluorescence (EDXRF), Scanning Electron Microscopy with Energy dispersive X-Ray spectroscopy (SEM-EDX) microanalyses and Micro-Infrared Spectroscopy (μFT-IR) techniques. In particular, the metallic elements present in the dyes where revealed through XRF and SEM-EDX, while μFT-IR gave details about organic binders. Elemental compositions obtained for the black decorations allowed to distinguish original parts of the fragments from those restored or remade.
The characterization of materials performed by our multi analytical approach, allowed us to get a deep knowledge of the technology of this ancient viol maker.
In particular, the varnishes are probably composed by a diterpenic and/or triterpenic resin. In the same way, in a few traces of glue the presence of proteinaceous substances have been individuated. As for the brush-decorated area, they present a preparation layer rich in feldspars on which a black layer of carbon black particles is applied. On the other hand the purfling areas are colored by an iron-gall dye. In particular the usage of a different ink allowed to identify restored areas.
Different imaging (UV-induced fluorescence, IR-reflectography, stereomicroscopy) and analytical techniques (XRF, μFTIR-ATR, optical microscopy, SEM-EDX) were employed to characterize both the materials of the painted decorations and those of the black wood purflings, of the varnishes and of the adhesives.
Materials and methods
In order to minimize any possible damage to the viol fragments, we decided for our analytical approach to be less invasive as possible. Our intent was to test and develop a procedure which could be also applied on integer instruments. For the same reason, we selected portable instruments, when available, which allow in situ examinations. To individuate and characterize the varnishes, the glue and the possible restored area (ante 1943), investigations by UV fluorescence technique have been carried out. The analytical campaign started with image analyses (namely UV and IR reflectography) in order to obtain an overlook of the materials. Infrared reflectrography measurements have been performed using a CEDIP Jade SWIR near infrared camera (HgCdTe focal plane array, spectral sensitivity 1000 to 2500 nm, 320 × 256 elements). The camera was equipped with a 50 mm macro lens. Samples were analyzed placing the camera at 10 cm distance with a circular illumination of incandescent light.
The analysis with UV-induced visible fluorescence was performed by means of preliminary direct observations and then photo shots were taken. The top plate was exposed to a Wood lamp with Philips TL-D 36 W BBL IPP low pressure Hg tubes (emission peak at 360 nm); the photo shooting of visible light fluorescence was carried out using a digital camera Nikon D90 with a Micro Nikkor 85 mm F3.5 objective, using a Kodak Wratten 2E filter (absorption at λ < 415 nm).
Non-destructive EDXRF analyses have been performed on the viol fragments with a portable spectrometer (Assing Lithos 3000) equipped with a low power X-ray tube with Mo anode and a Peltier cooled Si-PIN detector. A Zr transmission filter between the X-ray tube and the sample guarantees monochromatic radiation at Mo Kα energy (17.4 keV), with a 4 mm diameter collimator. The irradiated area on the sample is about 25 mm2. This means that for small details such as purflings, the irradiated area is larger that the one of interest. The distance between the sample and the X-ray tube is 1.4 cm; the same applies for the distance between the sample and the detector. The working conditions are 25 kV and 0.3 mA with a 100 s acquisition time.
In a second phase, several micro-samples, less than 1 mm2 size, have been collected with a cutter. All the micro-samples have been embedded in epoxy resin EpoFix Struers (curing time 12 hours, 15 parts of resin bisphenol-A-(epichlorhydrin)/2 parts of hardener triethylenetetramine) and then the cross-section observed using a polarized light microscope Olympus BX51TF, equipped with the Olympus TH4-200 lamp (visible light) and the Olympus U-RFL-T (UV light).
In order to characterize the organic compounds, on the cross sections and directly on some of the viol fragments μFT-IR analysis has been performed by the Nicolet iN10 Thermo Fischer μFT-IR spectroscope in ATR mode (Ge crystal). The IR spectra were collected in the range between 675 and 4000 cm−1 with a resolution of 4 cm−1, and subsequently expressed in absorbance units.
Images at higher magnifications of the samples were obtained through the FE-SEM Tescan Mira 3XMU-series equipped with EDAX spectrometer, at an accelerating voltage of 15–20 kV in high vacuum. The samples were made conductive with a coating of Au deposited with a sputter Cressington 208 HR. The elemental results have been obtained using the EDAX Genesis software processing.
Results and discussion
This section details the results obtained from the multi-analytical approach (μ-FTIR, SEM-EDS, EDXRF, UV fluorescence and IR reflectography) of the painted decorations, inlaid purfling, varnishes and adhesives. The information obtained by complementary techniques was combined to achieve the most complete knowledge of the materials and of the late renaissance lutherie technology.
Varnishes and glues
This result is fully compatible with the 16th century historical bibliography. In fact, different historical recipes are known, where diterpenic resin as sandarac and triterpenic resin as mastic were used as main components, generally melted in drying oils or solved, probably as in this case, in alcoholic solutions.
In the same way, traces of glue and samples of it were analyzed: the absorption bands of the spectra collected are characteristic of proteinaceous substances (1650, 1550, 1452 cm−1 Amide I, II, III; FTIR spectrum not shown). According to the wood-working and especially with the violin-making tradition, the use of reversible protein glues has always been very common. Between these ones, animal glues like rabbit glue and hide glue have always been the most widely used. The proteinaceous substance identified by infrared spectroscopy could be probably ascribable to one of these groups.
The viol fragments show traces of two different kinds of decorations: brush painted areas, especially present on the scroll and historically made with carbon black or black bone particles dispersed in an organic medium, and purfling inlays, on the upper block of the neck and on the back plate, generally made by black wooden strips colored by iron-gallic dye. In the following section, they will be discussed separately for sake of clarity.
Carbon black, if pure, should be deprived of elements detectable by EDXRF analysis; on the contrary, it is very absorbent of infrared radiation so that the infrared image obtained by IR reflectography can make its presence visible. Reflectography is widely used on painting for under-drawing examination. For this reason, there is a deep knowledge of the response of black painting media. We performed long wave infrared reflectography (with sensitivity ranging 1000–2500 nm) because, in this range of wavelength, carbon black pigments are strong absorber while iron-gallic ink are transparent . There are some other materials, such as hematite (iron oxide) which have instead an intermediate behaviour at these wavelengths. The iron-gallic dyes, on the basis of the ancient recipes, were produced by mixing vegetal extracts (tannins obtained by gall-nuts) with inorganic salts (mainly vitriols, nominally iron sulphates with other metal sulphates such manganese, copper, zinc, lead and others). For this reason, this kind of pigments is very well characterized by EDXRF analysis, but it is transparent to IR radiation.
The relation between metallic elements and iron, in fact, is the most important parameter for the characterization of iron dye chemical composition . Depending on the origin, the concentrations of the other sulphates listed above, compared with ferrous sulphate, in fact, can vary since the most ancient ingredients were not pure products. Moreover, ratios among the components are not explicitly quoted in ancient recipes and thus the final result can change a lot, the dye being a homemade product. For these reasons, the ratio between iron and other metals is often used to discriminate different iron inks .
The presence of a sort of inorganic ground layer under the carbon black film is remarkable. In fact, there are no historical references on the use of a ground layer under the decorations, in contrast with the varnish of musical instruments, where the presence of an inorganic ground layer is well known, especially during the 17th century, e.g. in many Stradivari’s violins . Following the opinion of many authors, as Sacconi quoted , the surface treatment of many string instruments of the so called classical period of Italian luthery (16th and 17th centuries) is a composite coating with at least two main distinct layers: the outer layer, composed of various varnish coats, is strongly colored and henceforth it can be called color varnish; the inner one is denoted as the ground layer, and is often identified as a hard, durable and insoluble material with good optical properties. According to recent studies and investigations based mainly on SEM-EDX techniques, the principal component of the ground layer of black decorations is a mineral micro- or even nanometric particulate with an organic binder.
The μFTIR analyses performed in different points of the decoration show absorption bands characteristic of amino and amide bonds, with stretching of NH at 3401 cm−1, C = O at 1655 cm−1 and NH2 at 1551 cm−1 (Figure 3B). The amino and amide bonds could be related to the presence of a proteinaceous medium of the decoration used as a binder of the carbon black pigment. The other absorption bands, and in particular those at 3360, 2926, 2855, 1709, 1451, 1382, 1170, 1038 and 887 cm−1could be ascribable to the resinous varnish already identified on the fragment surfaces, but could be also attributable to the cellulose of the wooden substrate under the decoration.
A final remark has to be done about iron–gallic ink and dye found by the combined use of in situ techniques (namely EDXRF and IR reflectography). The decorative edges are transparent to the IR radiation and the EDXRF analysis detects the presence of iron, copper and nickel (peculiar elements of iron-gall dyes). Taking into account Cu/Fe, and Ni/Fe ratios , we find a correlation except for one point corresponding to a restored area.
An analytical campaign on different fragments of a 16th century Viol was performed in order to characterize original materials of this ancient musical instrument. The results highlighted the possibility to get information about ancient materials as varnishes, glues, painted decorations and dyes used to color the inlays. The characterization of materials was performed by a synergic multi analytical approach, and it allowed us to get a deep knowledge of the technology of this ancient viol maker. At first step the analysis under UV light pointed out different visible fluorescence due to both varnish (especially along the less worn out part on the back of the neck) and glue (in the inner edges of the back plate) and allowed us to single out the points where non destructive analysis and microsampling could be performed. The combined use of EDXRF with IR reflectography performed on the inlay of the neck and the back plate detected the presence of an iron-complex dye used to color the black wooden purflings and a carbon black pigment used for the decorations of the scroll and the top plate fragments. These results are confirmed by SEM-EDX analysis that detected lighter elements.
The μFTIR analyses were performed on the varnishes layers identified by UV fluorescence imaging and diterpenic and/or triterpenic resinous substances, were individuated. Proteinaceous components in the junctions glues of the fragments were identified by μFTIR analyses: this result could be related to the presence of a bone black pigment or hide glue. Finally the analysis on the tuning pegs highlighted different decoration techniques and helped to confirm the hypothesis about the presence of restoration parts.
Scanning electron microscopy-energy dispersive X-ray microanalysis
Micro fourier transform-infrared spectroscopy
Attenuated total reflectance
Energy dispersive X-ray fluorescence
We would like to thank the Conservatorio Giuseppe Verdi in Milan for the collaboration and availability to improve this research, and Prof. Renato Meucci for his cooperation and precious advices. At last, we would like to share the memory of Federico Löwenberger, a great Italian contemporary viol maker.
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