I used up all my 22" x 30" watercolor paper, so today I started painting on Arches watercolor blocks. The important thing, when you're painting on paper, is that the paper not curl up. When using sheets, I tape them to pegboard, removing the tape only when the paintings are completely dry. With watercolor blocks, the sheets of paper are attached to a heavy board on the edges, and you remove them one by one after a completed painting dries. The blocks are stiff enough to set on an easel, which is how I paint.
I paint on these blocks "to the edge," which means they end up with no white space around them like my paintings on paper sheets (when the tape is removed, it leaves a white border). That's why I now prefer the sheets, but in these economic times I can't afford to buy more supplies before I use up the ones I have.
One of the 18 x 24 blocks I have is "hot-pressed" which gives the paper a smooth flat surface. The other is "cold-pressed" which means it has a rough texture. The paint has a slightly different effect on each surface.
My first effort on the watercolor block is very loose:
Nave of Hearts, 18" x 24"