Mr. Pottermack's Oversight by R. Austin Freeman

The efficient workman saves a vast amount of time by so planning out his job in advance that intervals of waiting are eliminated. Now Mr. Pottermack was an eminently methodical man and he was very sensible that, in the existing circumstances, time was precious. Accordingly, although his plan was but roughly sketched out in his mind, he proceeded forthwith to execute that part of it which could be clearly visualized, filling in the further details mentally as he worked.

The first thing to be done was, obviously, to convert the perishable, ephemeral footprints, which a light shower would destroy, into solid, durable models. To this end, he fetched from the workshop the tin of fine plaster of Paris which he kept for making small or delicate moulds. By the aid of his little lamp he selected a specially deep and perfect impression of Lewson's right foot, and into this he lightly dusted the fine powder, continuing the process until the surface was covered with an even layer of about half an inch thick. This he pressed down very gently with the flat end of the lamp, and then went in search of a suitable impression of the left foot, which he treated in like manner. He next selected a second pair of prints, but instead of dusting the dry plaster into them he merely dropped into each a pinch to serve as a mark for identifying it. His reason for thus varying the method was that he was doubtful whether it was possible to pour liquid plaster into a loam mould (for that was what the footprint actually was) without disturbing the surface and injuring the pattern.