When every particle of yellowness has disappeared, the fixing solution is drained off, and the surface _thoroughly_ washed, and it is then leaned against the wall to drain and dry. _Varnishing the Plate._ The plate, being thoroughly dry, is ready to receive a coating of transparent varnish.[K] in order to protect the albumen surface from injury during the printing process. To do this effectually the plate must be held before a fire, or over a lamp, until it is slightly warm all over; then pour over its surface the negative varnish, in the same manner as collodion is applied; allow the superfluous varnish to drain back into the bottle; hold the plate again before the fire until the whole of the spirit is evaporated; and, when cold, the plate is ready to be printed from, so as to produce any number of positive pictures on paper. [Footnote K: Humphrey's Collodion Gilding is the best for this purpose.] It will be observed, that in describing this process, the operator has been supposed to be so situated, that in case a second view of the same spot were required, he could return to his operating room, remove the plate which had been exposed, from the camera back to the plate box, and place another in the camera back, ready for taking another view. But, unfortunately, this is not at all times practicable. We, therefore, require some means of removing the plates, after being exposed, from the camera back into the plate box, and substituting others in their stead, whilst we are in the open air. In order to effect this, the "field plate box" has been devised by the author, by the aid of which the plates may be removed from the box, exposed in the camera, and again returned into the box, without any possibility of access of light falling on it.