With regard to MR. MABLEY'S process, described in "N. & Q.," No. 176., p. 267., as I am but a beginner myself, and have much to learn, I should be sorry to condemn it; but I should fear that his pictures would not exhibit sufficient contrast in the tints. Nor do I see the advantage the pictures would possess, if they did, over positives taken by our process. We amateurs in the country labour at present under great disadvantages, some of which I think the Photographic Society will remove. I am myself quite unable to form an idea what the collodion pictures done by first-rate photographers are like. All the positives done by amateurs in this part of the world, and developed by pyrogallic acid, which I have seen, present a dirty brown hue, by no means pleasing or artistic; and I have seen but very few, either developed by pyrogallic acid or protosulphate of iron, free from blemishes. I think if we were to act upon the suggestion made in "N. & Q." some time back, and send the editor a specimen of our performances, it would be a slight return for his endeavours in our behalf; and he would, I doubt not, honestly tell us whether our pictures were tolerable or not. I, for one, shall be very happy to do so. J. L. SISSON. Edingthorpe Rectory. _Developing Chamber._--I think MR. SISSON will find some difficulty in applying his very excellent idea of a sheet India rubber lighting medium to his portable laboratory, as the vapour of the ether will act upon it and render it sticky and useless after one or two usings. Allow me to suggest what I am in the habit of using, viz. a double layer of yellow glazed calico, stuck together with a little common drying oil, and allowed to dry for a few days: this causes a perfect exclusion of the actinic rays, and is very durable. F. MAXWELL LYTE. Falkland, Torquay. _The Black Tints on Photographic Positives._--A correspondent having inquired how these were obtained, and another replying that it was caused by starch, I beg to offer a process to your readers as to how they may obtain those carbonic tints; though I must premise that the process requires some skill, and is not always successful, though always sure to make them black: but on occasions of failure the lights sink, and the brilliancy of the picture is lost. That it is not starch in the French process, unless that vehicle contains some preparation, I am tolerably certain; the chloride of barium will often produce black images, though very uncertain; and the black process as given by Le Gray is uncertain also. For myself, I generally prefer the colour given by ammoniac salt; it is artistical and sufficient for any purpose. The present process, which I use myself when I require a black colour, with its imperfections, I offer to the photographic readers of "N. & Q.," and here it is.