Proof of Aggregation (IMAGE) Washington University in St. Louis Caption The absorption spectrum of a synthetic pigment in a polar solvent (magenta) that prevents the pigment molecules from forming assemblies differs substantially from the absorption spectrum of the pigment in a nonpolar solvent (blue). The difference shows that the pigments have the “hooks” they need to link up properly in solution. Credit Holten/WUSTL Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.