Abstract: A vacuum metallizing chamber cleaning procedure isolates the vacuum pumping system from the chamber, closes the chamber, sprays the interior of the closed chamber with water, then sprays the chamber with a caustic solution for a predetermined period dissolving aluminum deposits, then sprays with a neutralizer, and then sprays to rinse with water. Hydrogen is exhausted outside the building. The chamber is constantly drained during spraying. Caustic and neutralizer are recirculated. The sludge generated and removed during the cleaning operation is pumped from the bottom of a caustic holding tank to a settling tank for settling and subsequent re-use of the clear caustic solution.