Proteinaceous binders

M.P. Colombini, F. Modugno, Characterisation of proteinaceous binders in artistic paintings by chromatographic techniques, Journal of Separation Science, 27, 147 160 (2004). 

R. White, The characterisation of proteinaceous binders in art objects, National Gallery Technical Bulletin, 8, 5 14 (1984). 

Main Proteinaceous Binders Used in Art and in Historical Building Materials... 

A great part of the organic additives contains various amounts of proteinaceous materials. The identification of proteinaceous binder could help to explain the unusual properties of the mortars, such as high firmness, hydrophobicity of surfaces, and, for frescoes, high stability [24]. 

Recently, the above technique has been used for the identification of proteinaceous binders [27]. It was correctly anticipated that for each relatively well-defined protein... 

The choice of the appropriate time for the enzymatic cleavage is a critical point of sample preparation. All types of the reference proteinaceous binders (Section 6.2.3) were cleaved from 1 to 24 h at laboratory temperature 20 25 °C. The peptide peaks in the interval 900 2000 Da were registered below 900 Da the peaks of the matrix interfere and above 2000 Da the incompletely cleaved oligopeptides are present which makes interpretation difficult. The best result, i.e. the highest number of peaks, was obtained after digestion for 2 h at laboratory temperature [32]. 

In this section the experiments for the identification of proteinaceous binders contained in the model and artwork samples are summarised. 

Table 6.4 Composition of the proteinaceous binders in the model ground layers identified by peptide mass mapping...

Sample Proteinaceous binders Expected Found (score%) Measured peak m/z values... 

In the brackets the type of proteinaceous binder is specified according to experimental results. 

The type of proteinaceous binder was correctly identified in all model samples. In only one case (S10), the animal glue was additionally identified, although the restorer who prepared these model samples declared that the sample contained only egg binder. It is possible that this sample was contaminated during its preparation or during laboratory treatment. The results indicate that this method does not allow reliable identification of the presence of individual egg yolk and egg white most probably it is caused by the presence of a trace of egg white that is always present in the egg yolk preparations (and vice versa) and can be detected by the highly sensitive PMM method. The identification of individual types of animal glues will never be reliable by MALDI-TOF mass spectrometry because of their similar composition the application of ESI (electrospray ionisation)-MS/MS (Section 6.5) could possibly overcome this problem. Only the fish glue, whose peptide... 

The seven model mortar samples with proteinaceous binders and a blank were prepared in the authors laboratory and are described in Table 6.5. The binders were added to the basic mixture containing sand, lime and water (4 1 1 w/w/w). The samples were shaped into plates of dimensions 20x10x2.5 cm and left to dry under outdoor conditions. 

Proteinaceous binder Binder weight (g) Dry mortar mixture (kg)... 

Applications of PMM for the analyses of proteinaceous binders in artworks are summarised in Table 6.7 [21,39 43], The analyses of the most interesting paintings by E. Munch, are described in detail here. 

Artwork description Historical allocation Proteinaceous binder References... 

Painting (year) Sample code Layer description Proteinaceous binder... 

According to previous analyses of these paintings, the colour layers contain a high concentration of phosphorus (in the order of units of per cent) [40] this led restorers to the assumption that they contain casein which was ruled out by our detailed analysis. Thus, a high concentration of phosphorus coming from the proteinaceous binder is excluded because of the low concentration of phosphorus in the most phosphorylated binder (casein, max. 5% phosphoms) and the amount in the colour layer (up to 10%).The source of phosphorus was discovered by powder X-ray microdifffaction it comes from aluminium phosphate that was probably used as a substrate for the precipitation of red organic lake [40],... 

Several samples of materials from historical buildings have been analysed by the PMM method and the results are summarised in Table 6.9. In nearly all of them proteinaceous binders were reliably identified [32,44,45]. 

All these results have confirmed that the described methodology can be used for the identification of proteinaceous binders in solid samples taken from historical objects. The method facilitates the distinction of the basic types of proteinaceous additives (milk proteins from collagenous, etc.) that are contained in low concentrations in medieval or even older samples. 

The application of PMM enables the identification of proteinaceous binders in a more reliable and sensitive way than the more commonly used classical analytical methods. 

The fascinating experience with 1000-year-old mortar, in which the protein concentration was extremely low, has shown that by using this method it is possible to work in fields where other methods fail. In the case of easel paintings, small samples are usually available the advantage of the method described here also lies in the true microdestructive character. Moreover, as most samples, mainly in the case of paintings, often contain more than one proteinaceous binder (see e.g. E. Munch Portrait of Friedrich Nietzsche , Section 6.4.3), it is very encouraging that the PMM allows the simultaneous determination of at least two of them. 

M. Carbini, R. Stevanato, M. Rovea, P. Traldi, D. Favretto, Curie point pyrolysis gas chromato graphy mass spectrometry in the art field. The characterization of proteinaceous binders, Rapid Commun. Mass Spectrom., 10, 1240 1242 (1996). 

G. Chiavari, N. Gandini, P. Russo, D. Fabbri, Characterisation of standard tempera painting layers containing proteinaceous binders by pyrolysis gas chromatography mass spectrometry, Chromatographia, 47, 420 426 (1998). 

S. Kuckova, R. Hynek, M. Kodicek, Identification of proteinaceous binders used in art works by MALDI TOF mass spectrometry. Anal. Bioanal. Chem., 388, 201 206 (2007). 

In the case of paint samples where lipids are often admixed with proteinaceous binders, in some cases acidic hydrolysis is proposed to simultaneously hydrolyse proteins and triglycerides in the same step [35,36], although in acidic conditions the hydrolysis of triglycerides is not quantitative. 

Colombini M.P., Francesconi S., Fuoco R., Modugno F., Characterisation of proteinaceous binders and drying oils in wall painting samples by GC MS, Journal of Chromatography A, 1999,846,101 111. 

The proteinaceous binders are one of the main constituents of the wide range of organic materials and are a central component of the artist s palette. In the technique referred to as tempera, artists commonly used proteinaceous binders derived from egg, milk or casein, and collagen glues derived from animal skins or bones. These can be used independently, mixed together, or in a more complex mixture with siccative oils (as in the tempera grassa technique) or plant gums. 

The identification of the proteinaceous binder is done by the evaluation of the amino acid patterns obtained generally egg, casein, animal glue and garlic (garlic being used in gildings [93]) are reported. The amino acid profiles have been processed by different methods and several strategies have been developed to obtain the final identification ... 

In 1997 a collection of reference samples was prepared at the Opificio delle Pietre Dure of Florence by painting many glasses and wall specimens following Cennini s recipes using different pigments and proteinaceous binders. 

Use of correlation coefficients between amino acid profile data in order to efficiently quantify the degree of similarity between unknown samples and reference proteinaceous materials [7]. The method processes quantitative amino acid concentrations either as per cent relative content (pg g 1 %) or per cent molar content (mol %). A match of more than 0.9 is necessary to ensure a reliable identification of the proteinaceous binder. Table 9.3 reports results obtained on samples coming from the Tintori Collection analysed with two different analytical procedures showing a good correlation with the egg-based binder [96]. 

M.P. Colombini, R. Fuoco, A. Giacomelh, B. Muscateho, N. Fanelli, Characterisation of Proteinaceous Binders in Samples of the Giudizio Universale Wall Paintings at Florence Cathedral, Science and Technology for Cultural Heritage, 7(1), 49 58 (1998). 

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