The mode often followed is to immerse the Positive in the Hyposulphite Bath in the state in which it comes from the printing-frame; moving it about in the liquid in order to displace air-bubbles, which, if allowed to remain, produce spots. But the Author, for reasons given in the first part of the Work (pp. 129 and 165), recommends that the print should first be washed in common water until the soluble Nitrate of Silver has been removed.[47] This is known to be the case when the liquid flows away clear; the first milkiness being caused by the soluble Carbonates and Chlorides in the water precipitating the Nitrate of Silver. Greater security is thus afforded that the print will be toned in a really permanent manner, since after removing the Nitrate of Silver from the proof, the Bath does not work quickly unless the supply of Gold be well maintained. [47] This water must be free from Hyposulphite of Soda, or the print will become discoloured. Immediately on coming in contact with the Hyposulphite of Soda in the fixing and toning Bath, the chocolate brown or violet tint of the Positive disappears, and leaves the image of a red tone. Albumen proofs become brick-red; Ammonio-Nitrate a sepia or brown-black. If the colour is unusually _pale_ at this stage, probably the Silver Bath is too weak, or the quantity of Chloride of Ammonium or Sodium insufficient. After the print has been thoroughly reddened, the _toning_ action begins, and must be continued until the desired effect is obtained. This may happen in from ten minutes to a quarter of an hour, if the solution is in good working order and the thermometer at 60°; but much depends upon the temperature, and the activity of the Bath. English papers, and especially the same prepared with Albumen, tone more slowly than foreign papers plain salted. The brown and purple tints are an earlier stage of coloration than the black tones, and therefore the latter require more time. It must be borne in mind however that prolonged immersion in the Bath is favourable to sulphuration and yellowness; tending also to render the image unstable and liable to fade in the half-tones. This fading may not be seen decidedly whilst the print is in the Bath, but will show itself in the after-processes of washing and drying. The ultimate colour of the Print will vary much with the density of the Negative and the character of the subject; copies of line engravings, having but little half-tone, are easily obtained of a dark shade resembling the original impression. Some advise that on removal from the toning Bath the Print should be soaked in new Hyposulphite for ten minutes, to complete the fixation; but this precaution is not required with a Bath of the strength given in the formula. An analysis of an old Bath which had been extensively used, indicated only ten grains of Hyposulphite of Silver to the ounce, so that it was far from saturated.