_Remarks._--I put enough of the cyanide of potassium into the water to make the solution of such strength as to dissolve off the iodide of silver ("coating") in from twenty to sixty seconds. The operation is quite similar to that of hyposulphate of soda upon the coating of the Daguerreotype plate. A too concentrated solution is likely to injure the sharpness of the image. Brightening and Finishing the Image. [Sidenote: HUMPHREY'S COLLODION GILDING.] The article I now employ for finishing off my Positives is in market, and known as Humphrey's Collodion Gilding. It is a new preparation, and exerts a powerful influence upon the image, having the same brightening effect as chloride of gold on the daguerreotype. There is no article now in market that equals this. I have until quite recently used a varnish for this purpose, but having something that is of far greater value, I have discarded it. It is one of the most valuable improvements since the application of the Collodion Film as a vehicle for producing photographic images. It is a new discovery, and is being rapidly brought into use by the first ambrotypers and photographers in America. It adds at least one-half to the beauty of an ambrotype, above any method heretofore in use. It is _imperishable_, giving a surface almost equal in hardness to the glass itself. It is easy of application; it gives a brilliant finish; it is not affected by a moist atmosphere; it is not affected by pure water; it is the best article ever used for _finishing ambrotypes_; it will preserve glass negatives for all time; it will preserve the _whites_ in the ambrotype; it gives a rich lustre to drapery; it will bear exposure to the hot sun; it preserves positives and negatives from injury by light. It is an article that, when once tried, the operator upon glass (positive, negative, or albumenized plates) _will not do without_. The ingredients in the composition of this gilding are neither _patented_ nor _published_, but it can be procured from any dealer in photographic chemicals. Nitrate of Silver Bath. [Sidenote: NITRATE OF SILVER BATH.] I here give what I consider an improvement on the bath mentioned in the first edition of this work. I first published it in _Humphrey's Journal_, No. 23, Vol. VII.: The nitrate of silver solution is an important mixture in the chemical department of the ambrotype process, and requires the especial care of the operator in its preparation. I give the following as one of the most approved for general practice. It is well adapted to the production of positives, and its action is of great uniformity. Pure water 1 ounce. Nitrate of silver in crystals [neutral to acid test] 45 grains. Nitric acid C. P. [Quantity as given below]. This proportion is to be observed for any quantity of solution. If I were to prepare a bath 40 ounces, I would proceed as follows: