Specific surface area is more informative than grain size for fine-grained sediments where S s>1m 2/g. In fact, specific surface area plays a central role in engineering properties and processes in fine-grained soils including pore size and bioactivity; fabric, plasticity and rheology; hydraulic and electrical conductivity; compressibility and residual friction angle; and all forms of coupled processes. This research advanced a dye adsorption method using digital image colorimetry implemented with smartphone technology. In particular, adopted a water-based approach to reach internal surfaces in platy phyllosilicates, selected short dye molecules to reduce the range of potential molecular contact area, and developed a physics-based adsorption model to analyze the complete dataset to minimize the uncertainty in specific surface area determinations. The study involved fine-grained soils with distinct mineralogy and specific surface area (from 1 to 600 m 2/g), and various cationic dyes and a protein to explore the effect of molecular size and shape and pH effects. Crystal violet emerged as a reliable dye for soil characterization. Time-dependent measurements confirmed second order kinetics and highlight the importance of adsorption time.