Starting Friday, a stroll through one of Portland’s downtown squares may be accompanied by a live piano performance. Four pianos will be placed along Congress Street in Monument Square, Congress Square, Longfellow Square and Bramhall Square. Each was painted this week by local artists. The Pianos in the Square project aims to add artistic vibrancy to Portland, said director of parks, recreation & facilities, Sally DeLuca. Participants and staff at Bomb Diggity Art paint an upright piano on Wednesday.