_Glass jar Positives._--A good _white_ or light-green glass will answer for the collodion coating. Glass which contains air-spots can be used, if it be placed in such a manner as to let the light of the image come over them, as the spots cannot be seen through the opaque surface. Only the best white glass should be used for _covering_ the picture. Some operators use the convex glass, which is very clear, and answers the purpose. _The Nitrate of Silver Bath_ should be kept covered, except when in use. _If a Glass be Immersed too soon_, streaks and waves will be occasioned. These will be seen at the end of the plate which is least dry: the coating is also more liable to peel off. It should be borne in mind, however, that the peeling of collodion is not always attributable to this cause. _Diffused Light in the Developing Room._--In proportion as the sensitiveness of the plates increases, greater care must be exercised in thoroughly excluding all rays of white light. With opalescent films, neutral, this cause of fogging is more common than any other. _Tn the case_ of a portrait, if the features have an unnaturally black and gloomy appearance, the dark portions of the drapery, &c., being invisible, the picture has been _underexposed_ in the camera. CHAPTER VII. =HELIO PROCESS.=[F] [Footnote F: It has been thought advisable to publish in this work the _Helio Process_, and I do so just as it appeared in _Humphrey's Journal_.--S. D. H.] An Entire Process for Producing Collodion Positives and Negatives with one Bath, and in much less time than by any other known Process.--By Helio.--Photographic Patents. Boston, Oct., 1856. S. D. Humphrey. _Sir_,--As _Humphrey's Journal_ is the only truly progressive and independent Photographic publication in America, I feel it the duty of every one to aid its Editor in furthering the interest of the amateur and practitioner of the art; and, suiting the action to the word, I present the following Process as being worthy of confidence, and having, in my hands, proved eminently satisfactory. I am surprised to see that Operators and men respectably connected with the practice of the Art should so far fall beneath the station of true artists as to advertise to catch each other, or the verdant ones, by offering this or that little improvement all "printed complete for five dollars." As an amateur, and having the good of the science I love at heart, I now contribute my mite for the benefit of all interested; and, following the glorious example of G. B. C. (who I hope we shall soon hear from again,) in your last, I say--God speed! I shall endeavor to be as minute and concise as possible, so as to enable any one to adopt and successfully use my processes.