The etching or damping and rolling-up of the Collotype plate presents difficulties which are greater even than those met with in the preparation of the plate. These remarks also apply with equal force in photo-lithography, and whoever stops at the preparation of the plates or the photo-lithographic transfer, and leaves the subsequent operations to be performed by another, should not be considered either as a collotypist or photo-lithographer. The whole success depends upon a succession of apparent trifles; many errors it is impossible, or at any rate difficult, to rectify, and great care should be taken that nothing is overlooked, or from some trivial cause the whole may result in failure. Firstly, remove all adherent matter from the back of the plate, as the smallest amount of dried gelatine, particle of grit or other hard matter will suffice to cause the fracture of the strongest glass plate on the first application of pressure. =The Etching or Damping Solution= in most common use consists of a stock solution of five parts water, one part liquid ammonia, three parts glycerine, and one-tenth part of nitrate of lime. For use add five or six parts of this solution to 100 parts of water, sufficient of this being used to well cover the plate when placed in a clean dish. Another reliable formula is one litre glycerine, 600 cc. water, chloride of sodium three grammes. Plates may be immersed in these solutions for a time extending from ten minutes to five hours, or they may be well flooded with it, wiped off, and dried with blotting paper. The press having been examined, oiled, and put in thorough working order, the next consideration will be