IMMEDIATELY the picture, either positive or negative, has acquired its full development, the further progress of the action should be stopped. This is effectually accomplished by pouring over the surface, gently, a small quantity of a saturated solution of hyposulphite of soda.

The undecomposed iodide will quickly disappear, and the collodion, previously opaque, will become transparent and clear; the developed picture alone remaining; worked, as it were, by the power of light itself into the body of the collodion film. When the iodide of silver resists the action of the hypo-sulphite of soda, it can be assisted by pouring the latter on and off the plate several times; more particularly letting it, at each application, fall upon those parts of the picture requiring it most; but this must not be done too roughly.

The fixing is accomplished when the yellow opaque iodide of silver is gone; but it cannot always be perceived by looking on the surface, especially if the plate has been over-exposed to light, whether the iodide is entirely removed or not; consequently, it must be examined by being held up to the light, when any remaining yellow colour will be readily detected.

The drawing is now well washed with a stream of water from a lipped jug or vessel; the water should be poured gently from the middle of the plate towards the sides, to avoid, if possible, separating the collodion from the edges of the glass. After being well washed, the plate can be dried by a gentle heat, and varnished.


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