Modeling and Rendering of Metallic Patinas

Julie Dorsey and Pat Hanrahan

Submitted to SIGGRAPH '96

Abstract

An important component that has been missing from image synthesis is the effect of weathering. In this paper, we present an approach for the modeling and rendering of one type of weathering---metallic patinas. A patina is a film or incrustation on a surface that is produced by the removal of material, the addition of material, or the chemical alteration of a surface. Oxidation, sulphidization, and painting are examples of phenomena that produce patinas.

We represent a surface as a collection of layers. Patinas are simulated with a series of operators, such as "coat," "erode," and "polish," which are applied to the layered structure. The development of patinas is modulated according to an object's geometry and local environmental factors. We introduce a technique to model the reflectance and transmission of light through the layered structure using the Kubelka-Munk model. This representation yields a model that can simulate many aspects of the time-dependent appearance of metals as they are exposed to an atmosphere or treated chemically. We demonstrate the approach with a collection of copper models.

Additional information

PostScript of full paper without color plates (514KB).

Plate 1 (2MB).

Plate 2 (2MB)

Plate 3 (2MB)

Plate 4 (2MB)

Plate 4 Movie (760KB). This mpeq movie shows the buddha aging over a period of approximately 30 years. First a dark tarnish appears followed by the green patina.

Plate5 (2MB)

Last update: 10 January 1996
dorsey@lcs.mit.edu