Assessing Acrylic Inks: A Study of Colorants and Lightfastness

Abstract

Acrylic inks, derived from acrylic emulsion paints, have become increasingly favored by contemporary artists. These inks have advanced traditional watercolor techniques by improving water resistance and color intensity. This work presents the first systematic study on acrylic inks, focusing on synthetic organic pigments (SOPs) and their photodegradation behavior. A minimally invasive analytical protocol, requiring no chemical sample treatment, was developed on acrylic ink-on-paper mock-ups for direct SOP identification, combining μ-Raman spectroscopy and secondary ion mass spectrometry with MeV primary ions (MeV SIMS). Pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) was applied to selected mock-ups for binder and additive identification, which also influenced photodegradation. The examined acrylic inks were originally used by the Austrian caricaturist Erich Sokol (1933–2003) and manufactured by Schmincke, Rotring, and Winsor & Newton. Mock-ups were aged using a microfading tester (MFT) under LED illumination and analyzed before and after aging. For comparison, selected unaged ink mock-ups were displayed for one year under actual museum conditions. Despite the manufacturers’ claims of lightfastness, both procedures (MFT aging and museum display) revealed chemical changes in several SOPs. Results show SOP mixtures present in most acrylic inks. In some instances, one pigment within a mixture appeared to degrade faster than the others─e.g., PY13 relative to PY83 in yellow inks, or PY14 relative to PG36 and PY74 in green inks. The applied approach was verified on a minute sample from one of Sokol’s caricatures, demonstrating its effectiveness for minimally invasive SOP identification in modern and contemporary works on paper.