Etched Al of uniform quality is obtained at a const. rate by pptg. Al(OH)3 from the bath with simultaneous regeneration of the NaOH or KOH. The pptn. is promoted by addn. of Na2CO3. Filterability of the ppt. is improved by the addn. of complexing agents, e.g. Na gluconate. Thus, water 12 m3 at 40-60 Deg, Na2CO3 1000, NaOH 280, and Na gluconate [527-07-1] 6 kg were placed into container, dild. to 20 m3, mixed, and heated to .apprx.70 Deg. Hot etching was done at 70-75 Deg, pH 11.7 +- 0.1, and 6.5 +- 0.5 g Al/m2-min for 1-10 min. After treatment of .apprx.5000 m2 of Al, pptn. of Al(OH)3 began. The solid content was allowed to increase to .apprx.350 kg (corresponding to the treatment of another 5000 m2 of Al), and was then kept at 250-500 kg by continuous or batchwise filtration. The filter cake was washed with water, and the filtrate and wash water were recycled. The bath was maintained by periodic addn. of water, Na2CO3 100, NaOH 50, and Na gluconate 2 kg. [on SciFinder (R)]