Abstract: Long-term algicidal granules show improved color fastness over previously known granules. The granules have a ceramic coating comprising three layers, the first two of which have a copper compound such as cuprous oxide therein at relatively equal amounts. The ceramic coating further includes a third layer having pigment, a borate compound, and zinc oxide having an average particle size less than about 0.13 micrometer. In particular it has been found that the use of cuprous oxide allows conversion to black cupric oxide, which is more insoluble than cuprous oxide and black in color, allowing the algae-resistant granules to retain their original color for loger periods of time under weathering conditions. Methods of producing such ceramic-coated granular materials are also disclosed.

Abstract: A method of inhibiting algae growth on an asphalt shingle surface exposed to varying humidity using a blend of copper-containing algae-resistant granules and non-algae-resistant granules. The copper-containing algae-resistant granules comprise a substrate granule having at least one inner ceramic coating layer comprising cuprous oxide and a seal coating having a thickness covering the inner layer and which is at time t.sub.o devoid of copper.