“That is the reason they call this a negative,” Rex explained; “I think it means, not what it ought to be, because when this plate is dry, and we lay a piece of sensitised paper against it and put it in the sun, the print that comes off on the paper is called a positive; that is, we have a proof, a picture, as it ought to be.”
“What do you do now?” asked Nan, in an awed whisper.
“Why, now I take it out of the developer and plunge it up and down several times in this bucket ol water, to wash the developer off, and now I put it in this other tray; there's a solution of soda in here.”
“Solution of soda?” thought Harry. “Dear me! Regie does know a lot for a boy of his age.”
“What does the soda do?” he asked.
“It eats something off the plate, I think,” Regie answered, somewhat vaguely; “something I believe that ought to come off. And now I wash it thoroughly again, and now I put it in this third tray, which has a solution of alum in it. The alum gives the plate a good colour. Now another good washing and it is finished.” All this required much more time than it takes to write about it. “As soon as the plate dries we can print a proof from it,” Rex farther explained, “that is, if the sun stays out. Would you like to see me do the other one?”
“Like to see you!” said Nan, in a tone as though she wondered if Regie could possibly think for one moment that anything could at all compare with just this very thing that they were doing.