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The brush is to be filled under the tap. It is then used as a normal brush, with a light pressure on its side to let the water run.
A rag or a paper tissue is necessary to clean it when changing colors.
It works for details or small touches, but not for doing washes.
For the workshops at the Louvre, if you wish to use watercolor, you will need such a brush (no water jars allowed in the Museum).
