I bought 10 sheets of Arches Velin BFK Rives paper not knowing how it would work with watercolor. The label said "Art Publishing" with uses listed as lithography, screen printing, colotype, intaglio, relief engraving, letterpress, linocut, blind embossing and gold tooling but nothing about watercolor. The price was right for experimenting.
The surface was soft lending itself to gradient effects. The soft surface also worked well when scrubbing my brush into the paper pushing the paint out of the way. This worked to give the clouds the dark edges. The azure blue paint is Holbein "Irodori" Antique watercolor(another bargain) containing pigment PB15 pthalo blue and PW6 titanium white, which is opaque. I often use this when I get carried away with the ultramarine in the sky.