| 摘要 |
A layer (11, 12) of photosensitive material is formed on each face of a metal sheet (10), each face is exposed to light to form a design of exposed and unexposed regions which correspond to the perforations on one face and to the hollows (6) on the other face, chemical etching (14, 6) of each face is performed, and the photosensitive material (11a) is then removed from the front face and the etching is continued until the grid is completely perforated. <IMAGE>
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