Iridescent Reflectance Model for Pāua Shells

Abstract

<p>Haliotis Iris shells, commonly known as Pāua shells, are used in jewelry, decorations, and certain Maōri artifacts. Digital twins can be used to digitally preserve these objects, as well as accurately visualising them in media. Accurate representation of the Pāua material is essential to this process. Pāua shells are composed of a complex multi-layer microstructure which, due to Bragg diffraction, creates intensely colorful iridescence. Iridescence can also occur in various other material structures, and reflectance models to capture either general iridescence for these materials or highly specific iridescence, like for bird feathers and soap bubbles, have been developed. However, these models do no encapsulate the unique properties of Pāua shells. These previous models significantly limit the number of layers used, do not consider the natural thickness variation and gradient within the layered structure, and none consider the cyclic growth band structure responsible for the high contrast patterning of the shells when polished. Therefore, a specific iridescent reflectance model unique to Pāua must be developed. I propose an iridescent reflectance model specifically tailored to Pāua shells, accompanied by a texture to define the layers and pattern of the shell. The model fully simulates multiple layers given an adjustable threshold and a gradient for the layer thickness variation within each growth cycle. This model present a specific and complete solution to rendering Pāua shells which has not previously been done, as well as allowing for an input texture to realistically or artistically recreate the shell patterning.</p>