Da Vinci's Series 5040 Mottler is great for washes in watercolor and fluid acrylic, and for gessoing and varnishing. If you prefer a synthetic for these applications, this is as good as it gets.
Note — Brush sizes are not standardized. The length and width of a brush of a given shape and size varies considerably by manufacturer. Since fine art brushes are handmade, expect some variation even among brushes from a given manufacturer.
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