When he had made the trials and had added the new ingredients for future ones, he began to think out methods of his own which had suggested themselves to him of late, but which he had never been able to try.

But though he had the furnace to himself, to use as long as he could endure the heat of the advancing summer, he was face to face with a difficulty that seemed insuperable.
The furnace had but three crucibles, each of which contained one of the mixtures by means of which he and Beroviero were trying to produce the famous red glass.

In order to begin to make glass in his own way, it was necessary that one of the three should be emptied, but unless he disobeyed his orders this was out of the question.

In his train of thought and longing to try what he felt sure must succeed, he had forgotten the obstacle.

The check brought him back to himself, and he walked disconsolately up and down the long room by the side of the furnace.
Everything was against him, said the melancholy little demon that torments genius on dark days.