Connecting Chemical / Physical Properties and Material Appearance

The aspect of a material depends on its surface characteristics and on its chemical composition. The dependency on surface characteristics, such as surface roughness, is relatively well known.

The connection with the chemical composition is less well known. For example, both these pictures depict hematite, an iron oxide (Fe2O3):

Hematite (Crystalline form) Hematite powder

This color change is related to Mie scattering, the way light interacts with the smaller particles. Color depends on grain size. When the powder in included in a solvant (for oil painting), color also depends on solvant properties and concentration. Physical models explain the connection between grain size, concentration and color. The model is (obviously) non-linear. It is also computationally expensive.

The goal in this project is to predict the visual properties of a mixture of hematite powder and solvant, based on the physical properties of the mixture (grain size, chemical composition, solvant). This project will be done in cooperation with Institut Néel, allowing access to the actual properties of the materials, along with its color.

In a first step, we focus on hematite, because it is an interesting material and because it is present in many archeological sites, dating back to the neolithic. In a second step, we plan to extend the approach to other materials.