There is nothing to be seen on the glass just taken from the camera.

But there is a potential, though invisible, picture hid in the creamy film which covers it.

Watch him as he pours a wash over it, and you will see that miracle wrought which is at once a surprise and a charm,--the sudden appearance of your own features where a moment before was a blank without a vestige of intelligence or beauty.
In some such way the grave warnings of Master Byles Gridley had called up a fully shaped, but hitherto unworded, train of thought in the consciousness of Myrtle Hazard.

It was not merely their significance, it was mainly because they were spoken at the fitting time.

If they had been uttered a few weeks earlier, when Myrtle was taking the first stitch on the embroidered slippers, they would have been as useless as the artist's developing solution on a plate which had never been exposed in the camera.