A wall of Jell-O is slowly growing and collapsing — at the same time — at the Seattle Center. The jiggly wall about 5 feet high and 12 feet long is the work of artists commissioned for a three-week evolving exhibit to celebrate the 50th anniversary of the 1962 Seattle World's Fair. Artists Lisa Hein and Robert Seng will be adding rows of loaf-size Jell-O bricks through the Sept. 8 Seattle Center Big Birthday Bash. The artists cook up the gelatin on a hot plate and cool it in molds in a refrigerator on the site. Blueberry, raspberry, orange, cherry and blackberry bricks are held in place by a gypsum mortar that supports the wall as the Jell-O on the bottom melts.