Examination, conservation and restoration of painted art

Abstract

To conserve or restore painted artwork, it is necessary to appreciate the nature of the basic materials used in its creation, to be able to identify the pigments and the application media that were originally – or have subsequently been – applied and to understand the nature of gradual chemical and physical degradation that occurs within the various components of the system. With information thus gained, one can determine how best a painting may be cleaned, restored and ultimately be better preserved. This review covers the range of analytical techniques (mostly spectrographic), which have often been specifically developed to aid the identification of the wide range of inorganic colours and organic binders (or their degradation products) that may be present in each paint layer of an old masterpiece. Although an art gallery or museum strives to conserve the artefacts it displays, over time there will be varying degrees of mechanical or chemical damage. Cleaning (and, more controversially, restoration work) therefore becomes necessary and the much‐improved methods now available for achieving this without associated adverse effects are reviewed.

On the stability of mediaeval inorganic pigments: a literature review of the effect of climate, material selection, biological activity, analysis and conservation treatments

“…It promotes oil curing and it retards its oxidation [20]. Verdigris (neutral and basic), as well as the copper carbonate pigments azurite and malachite, shows the tendency to react with the oil binding media to form copper soaps [35,67,145], to brown and darken, as Cu + is formed by ambient light absorption (photoreduction), and oxygen promotes the formation of brown peroxide species [146]. Cu-salts of organic acidic compounds are formed in verdigris-containing paint layers (or at the interface with the varnish), as fatty and resin acids can extract copper ions from the verdigris pigment [133,147].…”

“…In oil, lead compounds were not only used as pigments, but as siccatives as well [219,220]. Moreover, lead soaps are formed in, or on the surface of, oil paint layers containing lead based pigments (leadwhite, lead tin yellow type I, litharge, red lead) and are investigated as they affect the appearance of paintings [54,55,107,145,[219][220][221][222][223][224][225][226][227][228]. Lead oxalates were observed on leadwhite treated with oxalic acid [32], and on real samples containing red lead and lead tin yellow [56].…”

Structural blue coating based on glaze painting

“…The observed discoloration in Rubens paintings due to aging is probably a consequence of the oil and/or varnish yellowing and to the increase of the refractive index of the binding medium that stiffens over time. Typically, the blue coloured glazes in easel paintings used ordinary blue pigments such as lapis lazuli, azurite, iron, or cobalt blue [5,6] .…”

“…For centuries, the secrets of famous Renaissance painters have stirred the curiosity of ardent art lovers. Some of their knowledge has survived until the present by being passed down through generations of art-restorers in transcripts of ancient texts [1,2] , complemented by the physical and chemical analysis of master paintings [3][4][5][6] . These advances in knowledge have economic consequences for the art market and can sometimes provide an inspiration to the science of material, as we propose here.…”

It must be green: meeting society’s environmental concerns

“…In the ancient world, man had to rely on two natural, copper‐based, mineral pigments that were green, namely malachite and verdigris [13], and these were of relatively low toxicity. Such was not the case for some of those that were subsequently produced synthetically.…”