Medium- and Long-Term Drying Effects in Tempera Paint Films Explored Through NMR Relaxometry Analysis

Area of Science:

• Art conservation science
• Materials science
• Biophysics

Background:

• Egg yolk tempera is a historical painting medium.
• Understanding its drying process is crucial for conservation.
• The role of binder composition and pigments in drying is complex.

Purpose of the Study:

• To investigate the long-term drying process of egg yolk tempera paint in the dark.
• To analyze the influence of water content, pigments, and drying time on paint properties.
• To characterize the structural changes within the egg yolk binder during drying.

Main Methods:

• Nuclear Magnetic Resonance (NMR) relaxometry and spectroscopy were employed.
• Proton (¹H) signals from egg yolk fatty acids were analyzed.
• NMR dispersion (NMRD) profiles were measured over 24 hours to 2 years.

Main Results:

• Increased water content (>50 wt%) led to egg yolk lipoprotein destructuration.
• Pigment characteristics (chemical nature, shape, surface area) also affected lipoprotein destructuration.
• A distinct, discontinuous change in NMRD profiles (a step) was observed around 1-2 months of drying.

Conclusions:

• The drying of egg yolk tempera paint involves significant structural changes over time.
• Water content and pigment properties critically influence the drying kinetics and binder stability.
• The observed time-dependent step change in NMRD suggests a phase transition or significant structural rearrangement within the paint film.