"That won't take very long," he said.
Meanwhile Hillyard busied himself with the second of the two white porcelain dishes. He brought out a cruet stand from a cupboard at the side of the stove and filled the dish half full of vinegar. He added water until the liquid rose within half an inch of the rim, and rocked the dish that the dilution might be complete. Next he took a new copying-pencil from the pen-tray on his bureau and stripping the wood away with his knife, dropped the blue lead into the vinegar and water. This lead he carefully dissolved with the help of a glass pestle.
"There! It's ready," he said.
"I, too," added Fairbairn.
He lifted out of the developing dish a wet sheet of writing paper which was absolutely blank. Not one drop of the black ink which had recorded those sentimental effusions remained. It was just a sheet of notepaper which had accidentally fallen into a basin of water.
"That's all right," said Hillyard; and Fairbairn gently slid the sheet into the dish in front of Hillyard. And for a while nothing happened.
"It's a clever trick, isn't it?" Hillyard used the words again, but now with a note of nervousness. "No unlikely paraphernalia needed. Just a copying pencil and some vinegar, which you can get anywhere. Yes, it's a clever trick!"
"If it works," Fairbairn added bluntly.
Both men watched the dish anxiously. The paper remained blank. The solution did not seem to work. It was the first time they had ever made use of it. The coast slid by unnoticed.
"Lopez was certain," said Fairbairn, "quite certain that this was the developing formula."