Rheological and structural characterization of emulsion-based paints

Area of Science:

• Art Conservation Science
• Materials Science
• Chemistry

Background:

• Historical emulsion paints, utilizing egg yolk and vegetable oil, were employed by artists from the 15th century onwards.
• Understanding the rheological properties of these paints is crucial for interpreting artists' techniques and material choices.

Purpose of the Study:

• To investigate the flow behavior and viscoelastic properties of modern emulsion paint recipes.
• To explore the influence of emulsion type (oil-in-water vs. water-in-oil) and pigment concentration on paint properties.
• To correlate microstructure with working properties for historical emulsion paints.

Main Methods:

• Preparation of oil-in-water (o/w) and water-in-oil (w/o) emulsion paints with lead-tin yellow pigment.
• Rheological measurements including steady shear flow and dynamic oscillatory tests.
• Confocal microscopy on model systems with glass microspheres to visualize particle localization.

Main Results:

• Stable emulsion paints were successfully prepared.
• Increased volume fraction of the dispersed phase led to higher yield stress, consistency, and viscosity.
• The continuous phase significantly influenced the viscoelastic properties of the paints.
• Confocal microscopy revealed preferential localization of pigment particles within one emulsion phase.

Conclusions:

• Paint preparation protocols directly impact microstructure and working properties.
• The findings provide insights into the material science of historical painting techniques.
• Emulsion type and pigment loading are key factors in controlling paint rheology.