CoverWell incubation chamber gaskets are expressly designed for immunocytochemistry and in situ hybridization. The chambers improve the uniformity and sensitivity of staining by enclosing a large sample area while minimizing the reagent volume required. The watertight seal holds reactants in place and prevents evaporation even during prolonged heating and is easily removed for multiple-step procedures. These chamber gaskets are heat resistant, autoclavable and nuclease free.