Abstract: Anodized aluminum surfaces are advantageously sealed by an energy- and time-saving two step process, in which the first step is contact at not more than 75° C. with a solution containing lithium and fluoride ions and, optionally, surfactant. The second necessary step is treatment with hot water or steam, which may be completed in considerably less time when only hot water or steam is used for sealing. Conventional smut inhibitors and/or neutral buffers as used in hot water for single step sealing may advantageously be included in the second step of this process. 100-1000 ppm concentrations of nickel and/or cobalt ions in the treatment liquid for the second treatment step, if environmentally tolerable, make it possible to complete this step in as little as 10 minutes at a temperature as low as 88° C.