Thanks to Tiffany for asking how
Large thin watercolor papers must be stretched, usually on a firm but thin wooden board. Stretching provides a smooth taut painting surface nicely fixed in place while you work. Small or very thick papers may not need stretching. How-to books and web sites advise total immersion of the paper by putting it into a tub of water. This inconvenient step is unnecessary if you follow my method.
Materials needed: The paper, board, acid-free gummed paper tape (not self-adhesive tape!) and a water spray bottle of the type used for wetting laundry or indoor plants.

1. Hold the paper to the light and check if there are watermarks on it. The correct surface of the paper treated for painting by the manufacturer faces you when the watermark reads correctly (not inverted).

2 . Use the water spray bottle to wet both sides of the paper thoroughly. The paper wrinkles badly as it expands. 3. Lay the paper on the board as evenly as possible without ever pulling it. Wait about ten minutes or more,
4. Cut out four lengths of gummed paper tape, each slightly longer than the corresponding sides of the paper. Make sure not to wet the tape at this stage. I store the roll of tape in an airtight container to prevent it sticking to itself in humid weather. It also helps to put a small pack of dehumidifier in the center of the roll. 5.Hold up a strip of gummed tape from one end and spray its shiny side with water, Rub the gum with the fingers down its length. Lay the end of the gummed tape halfway over the edge of the watercolor paper at one corner while holding the other end of the tap high.
6. Stretch the tape over the edge of the paper. Make sure the tape is half over the paper and half over the edge of the board before lowering it in place.. If the paper sticks in the wrong position lift it from one side and put it down again. 7. Pat the tape down over the paper and board by hand, or use a clean cloth or sponge.
8. When all the four sides are taped, place the board on a warm flat surface to dry. There is no need to wipe off excess water from the paper itself. 9. Depending on the weather it takes a few hours for the paper to dry out completely and become as tight as a drum.The use of a hair dryer on low power or a fan is possible, but only from a distance. Otherwise uneven drying and bulging may occur. If during painting the tape peels off, spray that part of the painting and use a bit of gummed tape to paste it back in place.

Remove the dry finished painting from the board carefully by inserting a knife point through the tape, then flat between the painting and the board. Never cut the watercolor paper itself. Slowly run the knife around the edge of the board. Or simply use a cutter at the paper edges.

The paper tape is removed from the margins of the finished painting by carefully wetting just the tape (and the edge of the paper behind it) with a large brush loaded with water. Then peel and scrape it off carefully without harming the painting itself.