After using the salt or the Ammonia, soak the Prints again for a minute or so in common water. Then place them in the toning Bath of Gold and acid; do not put in too many at once, and move them about occasionally, to prevent spots of imperfect action at the point where the sheets touch each other.
The foreign papers, plain salted, colour rapidly in two or three minutes. English papers require five to ten minutes; Albuminized, ten minutes to a quarter of an hour. The tendency of the Gold Bath is to give a blue tone to the image; hence proofs which are light red after using the salt or Ammonia, become, first red-purple, and then violet-purple in the Sel d'or. Albumen Prints assume some shade of brown, or of purple if not too strongly Albuminized. Ammonio-Nitrate papers highly salted, and prepared without Citrate, become first dark purple, and then blue and inky; the Citrate is intended to obviate this inky tint.
When the darkest tones are reached, the Bath produces no further effect, but eventually (more especially if the solution be not shielded from light [?]) there is a little decomposition, producing a cream-coloured deposit upon the lights.
The toning being completed, the Prints are again washed for an instant in water, to remove the excess of gold solution. This washing must not be continued longer than two or three minutes, or there will be danger of yellowness of the whites; this however ought not to happen with proper precautions.
Lastly, the proofs are fixed in a solution of Hyposulphite of Soda, one part to four of water; which may be used many times successively. This Bath alters the tone very little if the deposit of Gold be well fixed on the Print; but the writer has often observed in the case of Albumen paper and paper prepared with Citrate (Formula II.) that if removed too quickly from the Sel d'or, the purple tones change by immersion in the Hyposulphite to a chocolate-brown. Ammonio-Nitrate Prints are less liable to alter in this way.
In order that the fixing may be properly performed, the time of immersion should not be less than ten minutes with a porous paper, plain salted; or fifteen minutes in the case of an English or albuminized paper.
Ammonia may be used for fixing plain paper Prints; about one part of the Liquor Ammoniæ, to four of water. Ten minutes' immersion will usually be sufficient, and the tone is very little affected. This process is a good one, but the pungent smell of the Ammonia is an objection, and the Bath discolours by use. Some care too is required in order to ensure a proper fixing of the prints (see the remarks at [page 131]).
For directions to wash and mount the proofs, see [page 255].
It will sometimes happen in the Sel d'or process, from the toning Bath having but little solvent action on the light shades, that the Prints, after being washed and dried, appear too dark; this may be remedied by laying them for a few minutes in a very dilute solution of Chloride of Gold (five or six drops of the yellow solution of the Chloride to a few ounces of water) and washing for an additional quarter of an hour. Or an over-printed Positive may be saved by toning it with Chloride of Gold instead of Sel d'or. In that case, after proper removal of the free Nitrate of Silver, a few drops of a lemon-yellow solution of Chloride of Gold (with a fragment of Carbonate of Soda added to remove acidity, [p. 132]), should be poured over the Print, which is to be subsequently fixed in the usual way.