Toward Pigment-Free Leather: A Structural Color Design Framework Based on Photonic Crystal Principles

The large scale use of synthetic dyes in leather finishing raises growing environmental concerns and constrains long term colour stability. This conceptual study explores pigment free structural colour for leather based on photonic crystal principles and natural examples of structural colour. By transferring these optical mechanisms to fibrous leather substrates, we propose a multilayer L0–L4 surface architecture and a set of integration routes that embed periodic or quasi ordered nanostructures onto prepared grain. The framework links optical design parameters (feature size, refractive index contrast and angular response) with human factors requirements such as visual naturalness, glare acceptability and perceived premium feel. Rather than reporting experiments, the paper offers a design first roadmap and evidence seeking strategy for developing structural colour leather as a more sustainable complement to dye based colouration.