Possible Clues:

• Old agricultural worker upsets Charlie starting oil painting
• Forces (anag.)
• Picture of sales force dumping ales
• It's raw for the most part, and cold going around for the last supper, for instance
• Mural on plaster
• Sistine Chapel mural
• Work on a ceiling
• Picture painted on wet plaster
• Wet plaster painting
• Watercolor on wet plaster