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This etching/mezzotint has the characteristic velvety appearance, caused by the technique of the mezzotint
By polishing more or less it is possible to achieve different grey tones, or halftones, hence the name mezzo (half) tint. This depends on the skill of the engraver/artist. The technique allows for smooth transitions between the different grey tones. This gives the prints a velvety impression.
This is an ancient technique that Undabeytia has mastered
This etching is a P/A or a Prueba de Artista