Influence of Arsenic Compounds on the Colour Palette of 15th- and 16th-Century Icons from the National Museum in Cracow

Abstract

The National Museum in Krakow houses a collection of 15th- and 16th-century icons from the territory of the former Republic of Poland, distinguished by the presence of arsenic compounds both in the coloured layers of paintings, lights, as well as on the plain surface of backgrounds – which is rare. In historical treatises on painting, yellow arsenic sulfide – orpiment (As₂S₃) – in combination with indigo was used to obtain greens, and alone or in combination with whites to imitate gilding, including chrysography. Among the oldest Late Byzantine painting treatises, a background made with orpiment appears only in an Armenian manuscript. Mineral and synthetic forms of chemically unstable arsenic pigments, such as orpiment, realgar and pararealgar (As4S4
or AsS), degrade to partially transparent arsenic trioxide (arsenolite). The colour changes identified in colour mixtures, especially in the backgrounds of nine icons from the collection of the National Museum in Krakow, together with an analysis of technique and technology based on published research, allow in regard to four of them – the icon of Christ Pantocrator with Archangels (MNK XVIII-27) presented in more detail in the paper, as well as in the form of a supplement to the icons St John the Baptist and St Paul (from the Deesis, MNK XVIII-26), The Last Judgement (MNK XVIII-10), and The Last Judgement (MNK XVIII-32 ) – to assign them to the Armenian and South Balkan painting tradition.