A simple optical method is described that will enhance the color contrast between the outer birefringent hydration rind and the inner unhydrated core on obsidian thin sections used for hydration dating. The technique utilizes a gypsum accessory plate. The gypsum plate rotates all incoming light by 550 nanometers causing the black isotropic core of the obsidian to become transparent first-order pink and interacting with the transmitted light from the birefringent rind, by either addition or subtraction, to produce a second-order blue or a first-order yellow color. -- AATA