A method for testing a hollow sphere for the production of a piezoceramic hydrophone at least including: - the determination of a threshold value sw.1 from a predetermined maximum number of non-black-colored defects and/or a threshold value sw.2 of a size of non-black-colored defects and/or a threshold value sw.3 of the position of non-black-colored defects ; a.) applying an outer layer comprising silver and optionally silicon compounds on a first hemispherical shell and a second hemispherical shell ; b.) sintering and/or calcining the outer layer and obtaining a first coated hemispherical shell and a second coated hemispherical shell ; c.) combining the first coated hemispherical shell with the second coated hemispherical shell to form a hollow sphere ; characterized by : d.) plasma treatment of the outer layer and obtaining a plasma-treated hollow sphere with a black-colored outer layer ; e.) testing the black-colored outer layer for: - a number of non-black-colored defects and obtaining a first value w.1; and/or - a size of non-black-colored defects and obtaining a second value w.2; and/or - a position of non-black defects and obtaining a third value w.3 f.) comparing values w.1 with sw.1 and/or w.2 with sw.2 and/or w.3 with sw.3; g.) removing the plasma-treated hollow sphere if w.1 is greater than sw.1 and/or w.2 is greater than sw.2 and/or w.3 is greater than sw.3. - the determination of a threshold value sw.1 from a predetermined maximum number of non-black-colored defects and/or a threshold value sw.2 of a size of non-black-colored defects and/or a threshold value sw.3 of the position of non-black-colored defects ; a.) applying an outer layer comprising silver and optionally silicon compounds on a first hemispherical shell and a second hemispherical shell ; b.) sintering and/or calcining the outer layer and obtaining a first coated hemispherical shell and a second coated hemispherical shell ; c.) combining the first coated hemispherical shell with the second coated hemispherical shell to form a hollow sphere ; characterized by : d.) plasma treatment of the outer layer and obtaining a plasma-treated hollow sphere with a black-colored outer layer ; e.) testing the black-colored outer layer for: - a number of non-black-colored defects and obtaining a first value w.1; and/or - a size of non-black-colored defects and obtaining a second value w.2; and/or - a position of non-black defects and obtaining a third value w.3 f.) comparing values w.1 with sw.1 and/or w.2 with sw.2 and/or w.3 with sw.3; g.) removing the plasma-treated hollow sphere if w.1 is greater than sw.1 and/or w.2 is greater than sw.2 and/or w.3 is greater than sw.3. a.) applying an outer layer comprising silver and optionally silicon compounds on a first hemispherical shell and a second hemispherical shell ; b.) sintering and/or calcining the outer layer and obtaining a first coated hemispherical shell and a second coated hemispherical shell ; c.) combining the first coated hemispherical shell with the second coated hemispherical shell to form a hollow sphere ; d.) plasma treatment of the outer layer and obtaining a plasma-treated hollow sphere with a black-colored outer layer ; e.) testing the black-colored outer layer for: - a number of non-black-colored defects and obtaining a first value w.1; and/or - a size of non-black-colored defects and obtaining a second value w.2; and/or - a position of non-black defects and obtaining a third value w.3 - a number of non-black-colored defects and obtaining a first value w.1; and/or - a size of non-black-colored defects and obtaining a second value w.2; and/or - a position of non-black defects and obtaining a third value w.3 f.) comparing values w.1 with sw.1 and/or w.2 with sw.2 and/or w.3 with sw.3; g.) removing the plasma-treated hollow sphere if w.1 is greater than sw.1 and/or w.2 is greater than sw.2 and/or w.3 is greater than sw.3. <EOS>