I must close this, for I fear I have now exceeded the limits which your valuable paper may, with justice to others, spare to subjects of this nature. WILLIAM HARDY. * * * * *{157} PHOTOGRAPHIC CORRESPONDENCE. _Lining of Cameras._--I find nothing so good to line a camera with as _black velvet_; for, black the inside of a camera as you will, if it is hard wood or any size used, there will be reflection from the bottom, which, with very sensitive plates, gives a dulness which, I think I may say, is caused by this reflection. I think even the inside of the lens tube might advantageously be lined with black velvet. W. M. F. _Cyanuret of Potassium._--I have been using lately 12 grs. of cyanuret of potassium in 1 oz. of water for clearing the collodion plates, instead of hypo. There is one advantage, that there are no crystals formed if imperfectly washed, which is too common with hypo. You must take care to well wash off the developing fluid, whether pyrogallic, protonitrate, or protosulphite: if you use the latter 40-grains strong, the _whitest_ pictures can be obtained, nearly as white as after bichloride of mercury. A good formula to make it is-- Distilled water 11 drachms. Alcohol 1 drachm. Nitric acid 20 minims. Protosulphate of iron 60 grains. This I know to act well with care, and it will keep a long time. I find protonitrate solution-- Water 1½ ounce. Barytes 150 grains. Protosulph. 150 " mixed in a proportion of 8 to 4, with a 3-grain solution of pyrogallic--a very nice developing mixture; and, if poured back again after being used, will suffice 6 or 8 times over; but it is _best_ new. W. M. F. _Minuteness of Detail on Paper._--Being fond of antiquarian studies, and having learned from "N. & Q." the value of photography to the archæologist, I have serious thoughts of taking up the practice of the art. Before doing so, however, I am anxious to learn how far that minuteness of detail which I so much prize, and which is of such value to the antiquary, is to be obtained by any of the processes on paper. I have seen some specimens produced by collodion which certainly exhibit that quality in an eminent degree. Is anything approaching to such minuteness attainable by any of the Talbotype processes? F. S. A. [Had this Query reached us last week, we should then, as now, have replied in the affirmative. We should then have referred, for evidence in support of our statement, to Mr. Fenton's Well Walk, Cheltenham, published in the _Photographic Album_, and to Mr. Buckle's View of Peterborough. But we may now adduce a work almost more remarkable for this quality, namely, a view of Salisbury, by Mr. Russell Sedgefield, a young wood engraver, which is about to appear in the forthcoming part of the _Photographic Album_.