Many ways have been devised for putting up pictures I have produced pleasing effects upon colored glasses: for instance, a picture on a light purple glass has a very pleasing effect; also in some other colors. I have also used patent leather for backing the image. I have produced curious and interesting results by placing a piece of white paper, or coloring white the back of the _whites_ of the image, and then blackening over or around this. By this means the whites are preserved very clear. _Positives for Pins, Lockets, etc._--I employ mica for floating the collodion on, as it can be as easily cut and fitted as the metallic plate in the daguerreotype; and positives taken upon fine, clear, transparent mica, are fully equal to those taken upon glass, and yet they are ambrotypes. Mica is an article familiar to every one, as being used in stoves, gratings, etc. The method of using it, is to take the impression on a thick piece, and then split it off, which can readily be done in the most perfect, thin, transparent plates; it is equally as thin as tissue paper, and can be cut as easily. The thickness of the piece upon which the impression is taken is of no moment, since it can be reduced at pleasure and is more easily handled while thick. Observations on the Positive Collodion Process. Fogging.--There are numerous causes which will produce fogging: the principal ones will be mentioned. One is the admission of light upon the collodion. This maybe from a want of closeness of the dark room, the tablet,[E] the camera, or by accidental exposure. The method to locate the particular cause is to, _first_, when the glass is taken from the nitrate bath, let it stand for sufficient time to drain, then pour on the developer, and if the coating assumes a mistiness, or light-grey color, the fault is in the dark room; again, if the plate, after it has been treated with the developer and fixed, is clear, then also the fault is there. Now try the tablet in the same manner, and if not there, try the camera, and the proper location will be found. [Footnote E: Since the foregoing pages have been in type an entirely new feature in the line of apparatus has been introduced; this is W. & W. H. Lewis's Patent Plate-holder with solid glass corners. These Holders have every requisite for excluding the light from the sensitive surface; they are accompanied with a "shut off," so that when the slide is drawn no light can reach the glass. This, in connection with the unequalled advantage of the solid corners, makes them the most desirable article for the Operator. _Humphrey's Journal_, in referring to these Holders, says:--