The detachment of barnacles (under shear and tensile loads) from silicone was investigated with the aid of high-speed digital video recording. A handheld probe was used to apply loads to the shells of barnacles attached to three clear silicone-elastomer coatings of known thickness applied to glass plates. The tests were performed in the laboratory in air and underwater. Representative data are presented as a qualitative description of separation at the barnacle adhesive-silicone interface. Detailed examination of adhesive separation during detachment provided new insight into the nature of a marine biological adhesive on a low modulus, artificial surface. The visible response of the barnacle adhesive on silicone under external shear and tensile loading was suggestive of the viscous fingering seen in Saffman-Taylor instabilities. Complex branching separation occurred in rapid progression, usually within 100 ms. The results suggest that the barnacle adhesive exhibits rheological responses of a viscous material at the interface with silicone surfaces. Additional experiments with time-lapse photography demonstrated that the adhesive was stable underwater but became dehydrated or coalesced when exposed directly to air. A simple model of the adhesive system of a barnacle in contact with silicone based upon Balanus eburneus is proposed to assist in the development of a more complete understanding of barnacle adhesion.