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This etching/mezzotint has the characteristic velvety appearance, caused by the mezzotint technique
By polishing more or less it is possible to achieve different gray tones, or half-tones, hence the name mezzo (half) tint. This depends on the skill of the engraver/artist. The technique enables smooth transitions between the different gray 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