FLORENCE – Martin Bridge of Chesterfield works on a mural on the south wall of Pivot Media in Florence on Thursday. To celebrate the business’s 20th anniversary, owner Jim Gipe commissioned Bridge and his twin brother Carl, both teachers at the Pioneer Valley Performing Arts Charter School, to create a new historical mural that draws upon a span of mid-nineteenth century Florence before the Mill River flood of 1874. It references Sojourner Truth and the Northampton Association of Education and Industry’s utopian community, the Florence Sewing Machine Company and the Corticelli Silk Company – which ran advertisements featuring a cat playing with a spool of silk and the tagline “Too Strong to Break”.