_Processes upon Paper._--The favourable manner in which the account I have given of the Collodion process has been received, not only by your readers in general, as has been evinced by many private letters, but also by the numerous correspondents it has drawn forth, induces me, after some little delay, to request space for a description of the following processes upon paper. In giving these I wish it to be understood that I may offer but little that is original, my object being to describe, as plainly as I possibly can, these easy methods, and to make no observation but what I have found to be successful in my own hands. I have had the good fortune to obtain the friendship of some of the most successful photographers of the day; and taking three very eminent ones, I find they have each some peculiarities in his mode of manipulation, varying with each other in the strength of the solutions employed, and producing results the most agreeable to their respective tastes. Reviewing these different processes in my own mind, and trying with patience the various results, I conclude that the following quantities are calculated to produce an adequate degree of sensibility in the paper, and yet to allow it to be prepared for the action of light for many hours previous to its use, and yet with more certainty than any other I am acquainted with. I think I may always depend upon it for twenty-four to thirty-six hours after excitement, and I have seen good pictures produced upon the third day. I believe it is a rule which admits of no contradiction, that the more you dilute your solution, the longer the excited paper will keep; but in proportion to its diminished sensibility, the time of exposure must be prolonged, and therefore I am, from this waste of time and other reasons, disposed to place much less value upon the wax-paper process than many do. The process I am about to describe is so simple, and I hope to make it so intelligible to your non-photographic readers, that a perfect novice, using ordinary care, must meet with success; but should I fail doing so upon all points, any information sought through the medium of "N. & Q." shall meet with explanation from myself, if not from other of your experienced correspondents, whose indulgence I must beg should the communication be deemed too elementary, it being my earnest desire to point out to archæologists who are desirous of acquiring this knowledge, how easily they themselves may practise this beautiful art, and possess those objects they would desire to preserve, in a far more truthful state than could be otherwise accomplished.