Watercolor Postcard Paint-Along: Sketching with Watersoluble Line

Super-simple and minimal supplies: a watersoluble pen, a wet brush and a postcard or sketchbook. This is basically a form of line-and-wash, but doesn't seem to be taught or discussed much. My favorite super-lightweight sketching strategy.
For suggestions about protecting your postcards in the mail, please see the intro portion of the "Backlit Clouds Variations" postcard paint-along: • Watercolor Postcard Pa...
Supplies used in Postcard Paint-Along videos:
-watercolor paper: I cut scraps to postcard size (4x6"). I'm using 140-lb cold-pressed, 100% cotton watercolor papers, many different brands. This is how I use up paper samples and odds and ends. If you are new to watercolor, here are some popular 100% cotton papers to try: Arches, Saunders Waterford, Kilimanjaro (Cheap Joe's house brand), Dick Blick Premier (Dick Blick's 100% cotton house brand). A 22x30" sheet will yield 25 4x6" postcards.
-other supplies: I describe the items in my travel sketching kit in this video, for those who want more info about what I'm using: • Second Sunday Live Dem... . The video description for that video includes a link to a handout listing all the supplies, as well.