RESUMEN
Our diverse world cultural heritage encompasses a vast range of objects, from fi ne art to monumental cultural heritage sites, which represent not only artistic developments but also power, politics and commerce. They are combinations of materials and cultural infl uences that vary over time and according to style, taste, region and artist or workshop. The careful study of how an artwork is made is critical to its preservation: correct identifi cation of materials can guide conservators in treatments but also can direct curators and conservators in display and storage strategies. This identifi cation can also help reveal working practices of the artist, studio or guild: for example, the use of egg tempera, egg mixed with oil or only oil as a binding media in paintings marks a distinct alteration in working practice in Italy in the mid to late 15th century (Dunkerton 1996; Higgitt and White 2005). Furthermore, the identifi cation can also give insight into the trade customs of a town or region and, in some cases, may facilitate authenticating, dating, and determining the regional provenance of an object. For example there are pigments that were only used over certain time periods or became commonly used only later in the 19th century: thus their presence, in conjunction with other supporting evidence, can aid in determining the likely date of origin for an artwork. Scientifi c examination is critical in providing this knowledge and is an essential component in modern technical studies of artworks and cultural heritage. Throughout history a great variety of natural products have been used in art and one of the most common applications of organic materials has been as binding media, adhesives and varnishes1. Mixed with pigments they form the basis for paints (binding media), as adhesives they allow solid joints in furniture, and as varnishes they supply protective coatings for paintings, wood, and other decorative surfaces. Animal and plant materials used in art as binding media and adhesives include oils, waxes, resins, gums, mucilages and proteins. Eggs, milk, and animal glues (made from bones, skin, or fi sh bladders) composed primarily of the proteins ovalbumin, casein, and collagen — can not only be found in artworks but are also used to conserve art. Plant gums such as gum tragacanth2, cherry gum, and gum arabic, known as polysaccharides, have been used mainly as binding media for water soluble paint. Analysing the binding media and adhesives on artworks presents unique challenges. The natural materials, which can be used individually or in combination, are actually complex chemical mixtures whose composition can alter over time due to human intervention (e.g. conservation treatments), environmental conditions (heat, light, humidity, biodeterioration), and chemical interactions between the components of the mixture.In addition, the organic material can be encased in a complex solid matrix, such as pigments, and its concentration in that matrix tends to be very low. Furthermore, the original organic binder or adhesive may itself be a mixture (multiple protein sources or oil and protein mixture, for example) or may have become so via the migration of materials, for example between layers of paint during conservation treatment with adhesives or the application of coatings. And fi nally, that a sample of the artwork is required in order to identify proteins and gums dictates that the analytical techniques be.