fish eye

1. n. [Drilling Fluids]
A slang term for a globule of partly hydrated polymer caused by poor dispersion during the mixing process (commonly a result of adding the product too fast). Fish eyes are typically 0.2 to 0.5 inches in size and consist of a granule of unhydrated polymer surrounded by a gelatinous covering of hydrated polymer, which prevents water from entering to complete the hydration process. Thus, once formed, fish eyes do not disperse and the product is removed on the shaker screens and wasted.
See: microgel