Paints lipids

Chemicals are ubiquitous as air, carbohydrates, enzymes, lipids, minerals, proteins, vitamins, water, and wood. Naturally occurring chemicals are supplemented by man-made substances. There are about 70000 chemicals in use with another 500-1000 added each year. Their properties have been harnessed to enhance the quality of life, e.g. cosmetics, detergents, energy fuels, explosives, fertilizers, foods and drinks, glass, metals, paints, paper, pesticides, pharmaceuticals, plastics, rubber, solvents, textiles thus chemicals are found in virtually all workplaces. Besides the benefits, chemicals also pose dangers to man and the environment. For example ... 

The fatty acid percentage composition of some fresh lipids which may be encountered in an archaeological context or in a painting is reported in Table 1.3. 

Egg yolk and white were used in paintings either separated or, more often, together. Egg or egg yolk temperas served as the most common protein binders in colour layers of artworks. Egg white alone was used in book illustrations, but it was usually not involved in other artworks because colour layers containing it were too fragile. Egg yolk in temperas has always been popular because of the higher content of lipids, which make the layers elastic and increases their adhesion to the surface. 

This chapter gives an overview of GC/MS analytical procedures used for lipid determination, and a summary of the complex issue of lipid chromatographic data interpretation in paintings and archaeological objects. Some examples and case studies are also included. 

In the analysis of paint samples, a stepwise extraction of the various lipid and resinous components has been proposed [33] which uses isooctane, methanol, chloroform/methanol (7 3) and methanol/oxalic acid (10%). The last extraction releases FAs from the metal soaps. 

A specific sample pretreatment can be used to analyse lipids and proteins in a single paint microsample. This entails extracting proteinaceous matter with ammonia solution to... 

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. 

The analysis of paint samples represents a peculiar case, in which the identification of lipids is made virtually possible by the fact that the range of used materials is limited to drying oils (linseed, poppy seed, walnut, tung), egg yolk, and beeswax. Safflower oil (from... 

Lipids are generally identified in paint samples by evaluating characteristic ratio values of FA amounts and comparing them with naturally or artificially aged reference paint layers. Molar or weight contents are obtained after quantification based on calibration curves. 

The ratio between the amounts of azelaic and palmitic acids (A/P) is a parameter for differentiating drying oils from egg lipids in paint samples because the amount of dicarboxylic acid formed in the ageing of egg lipids is considerably less than it is in drying oils. Values of A/P >1 indicate a drying oil, values of A/P <0.3 are typical of egg lipids,... 

The ratio of oleic acid to stearic acid (O/S) is another parameter used for assessing the degree of ageing of a lipid paint binder. This ratio is considered as an index of oxidation because the oleic acid double bond is particularly reactive towards oxidation, so normally the content of oleic acid in aged paintings is very low, with an O/S value around 0.1 0.2 [55]. 

The differentiation of lipid media in samples from artworks on the basis of their sterol content has been attempted, but the tendency of sterols to oxidize means that they can rarely be detected in thin paint layers [56]. 

The following subsections describe some case studies dealing with GC/MS procedures used to investigate lipid materials in archaeological objects and paintings. 

Case Study 3 Characterization of Lipid Paint Binders in Paintings... 

To show some examples of the many cases of lipid paint materials reported in the literature, Table 7.3 reports the results of characteristic parameters obtained in the quantitative analysis of FAs in a series of samples (<1 mg) from paintings on various supports. 

The analytical techniques proposed in the literature generally give reliable information on lipids present in the paint layer. However, the presence of lipid mixtures and of particular environmental conservation conditions may affect the lipid pattern to such an extent that their identification may be very difficult and sometimes erroneous. Thus, a multianalytical approach is recommended which integrates chromatographic data with techniques such as mapping based on Fourier transform infrared spectroscopy or SIM on cross-sections, in order to better understand the distribution of lipids in the various paint layers. 

Schilling M.R., Khanjian H.P., Carson D.M., Fatty acid and glycerol content of lipids. Part II. Effects of ageing and solvent extraction on the composition of oil paints, Techne, 1997, 5, 71 78. 

G. Chiavari, D. Fabbri and S. Prati, In situ pyrolysis and silylation for analysis of lipid materials used in paint layers, Chromatographia, 53, 311 314 (2001). 

K. Keune and J. J. Boon, Enhancement of the static SIMS secondary ion yields of lipid moieties by ultrathin gold coating of aged oil paint surfaces, Surface and Interface Analysis, 36, 1620 1628 (2004b). 

Bilayer lipid membranes (BLMs) 2D, 3D 30- to 50- Painting of the surfactant (or A-thick, 1- to 2- lipid), dissolved in a hydrocarbon mm-diameter mem- solvent, across a teflon pinhole brane, supported which separates two by a solvent compartments of aqueous solution surfactant reservoir the Plateau-Gibbs border or torus) and separating two aqueous solutions macroscopically Hours Convenient system for fundamental studies as simultaneous electrical and spectroscopic measurements were possible 385, 387... 

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