The crossword solution for the term BLACKENS WITH GOO is TARS, which is an acronym for tar-asphalt roofing. Tar-asphalt roofing is a type of roofing material that is composed of asphalt and tar, which are heated and mixed together to form a thick, sticky substance. This substance is then applied to roofs in order to waterproof them and protect them from the elements. The tar-asphalt mixture also has the added benefit of darkening the roof, giving it a blackened appearance.