Preliminary Investigations into the Alteration of Cadmium Orange Restoration Paint on an Ancient Greek Terracotta Krater

Abstract

In preparation for exhibition, an ancient Greek terracotta krater received treatment which included selective in-painting with cadmium orange (CdSSe). After one year on display the object displayed disfiguring alteration in select areas of restoration. Cross-section analysis of samples taken from the object revealed that alteration only occurred in areas where the paint was in direct contact with darkened and abraded areas of the terracotta surface, in which analysis found the presence of chlorine. The alteration was recreated in mock-ups for more in-depth analysis. Using Raman spectroscopy and scanning electron microscopy with energy-dispersive X-rays (SEM-EDS) it was discovered that selenium-rich structures were forming throughout the paint films. The observed alteration is the result of degradation of the CdSSe pigment which occurs in the presence of chlorine and light. This research highlights the need for careful selection of restoration materials when dealing with objects suspected to contain residual chloride ions if desalination cannot be undertaken.

Deeper insights into the photoluminescence properties and (photo)chemical reactivity of cadmium red (CdS1−xSex) paints in renowned twentieth century paintings by state-of-the-art investigations at multiple length scales

“…In the field of heritage science, the discoloration of CdS 1−x Se x has been documented recently only in an ancient Greek terracotta krater, where the pigment was used as a restoration material. In this specific case, light and chlorine species were identified as two possible triggering factors of the alteration process [41].…”

Colour Analysis: An Introduction to the Power of Studying Pigments and Dyes in Archaeological and Historical Objects

“…The implication of scientific investigation on conservation and display decisionmaking is also treated in Rayner et al's contribution [11], which focuses on an ancient Greek terracotta krater treated with selective in-painting with cadmium orange (CdSSe). Some of the restauration areas showed alteration after one year from the application of cadmium orange.…”