THE PHOTOGRAPHIC NEWS. Oct. 8, 1858, p.59
Tewkesbury asks the cause of--First, long yellow metallic lines, and circles of the same colour, which are So frequently to be met with on removing the print from the printing frame, and which are still apparent after toning and washing. Canson's, and Papier Rive, are both affected with them, and Tewkesbury hardly ever gets a print faultless in this respect. Secondly, which chlorides are best adapted for preparing plain paper--chloride of ammonium, barium, or sodium?--1. The stains referred to are frequently met with in positives on albumenised paper. A little care in attending to the following points will obviate them. Use quite fresh eggs, and take care that the prepared albumen does not contain any opaque stringy particles suspended in it. The paper must also be lowered on to the surface by means of a steady, continuous movement. Any stoppages in this operation will produce bronzed lines across the paper. Carefully examine the surface of the albumen in the bath after each sheet has been removed from it, and if any scum appears on the surface of the liquid, remove it by drawing a piece of paper gently over the surface, before laying down the next sheet. Be careful also that the quantity of albumen in the bath be sufficient to prevent the sheet from touching the bottom. 2. It matters little what chloride be employed, provided the proportion be such that the bath contains the proper quantity of chlorine. The chemical reaction which takes place between the chloride used in the first preparation of the paper, and the nitrate of silver used in rendering it sensitive, is to produce a chloride of silver in the pores of the paper, which is the real photographic agent, and a nitrate of whatever base has been used in the first bath, be it ammonium, barium, or sodium. This nitrate is perfectly soluble in water, and consequently dissolves out into the silver bath whilst the sheet is being made sensitive, and we do not believe it has the slightest direct influence on the result. It may possibly slightly influence the picture in an indirect way, owing to the accumulation of the foreign nitrate in the silver bath which might thus, in the case of nitrate of soda, for instance tend to give a deliquescent film on the sensitive paper. Or from the chemical affinities of the base in question,--thus chloride of barium as a salting bath would tend to convert any sulphates in the paper to the state of sulphate of baryta, which is, as far as present experience shows us, perfectly harmless in a photographic point of view.