Possible Clues:

• Inscribed decorative characters
• Left making improvements, removing black text
• Stencil work
• By the sound of it, allow 'er to phone for what's been written
• Calligrapher's skill
• Granted, Wagner's operas will have no opening for happy characters
• Sounds as if this might permit 'er to telephone in writing
• It's 21 across that sounds as if it will allow her to operate in 1 across