A park-sized canvas and 1,000 pounds of chalk? Sounds like the recipe for a masterpiece, or in this case, 240 of them. That’s how many sidewalk squares frame midtown’s small but mighty Fremont Park, each waiting to be transformed into ephemeral works of art, with the proceeds, via sponsors, funding art supplies for area teachers. Now in its 35th year, the annual Labor Day weekend festival draws throngs to watch hundreds of artists create these alfresco frescoes with nothing but chalk. With thousands in attendance each year, expect this fest to be the chalk of the town all weekend long.