Possible Clues:

• First trick
• Liquid evidenced by the answers to this puzzle's starred clues?
• Means of secret writing ... or a description of a 17-Across?
• ?
• Prankster's item, and this puzzle's theme
• -
• Secret-message liquid
• Practical joke #1
• Gag for a typist
• 34-Down for a stenographer?