Related Clues:

• Sine
• What quills are dipped in
• Fingerprinting fluid
• Stamp pad stuff
• Shirt-pocket stainer
• Prepare, as a press
• Calvin Klein insider to put pen to paper
• Octopus's release
• Octopus's secretion
• What fills a pen
• It fills 21-Down
• Filler for 26-Across
• Filler for a pen
• It fills pens
• It's in a pen