After removal from this poor-quality backing, the print was humidified and then placed in a bath of purified water. The water was replaced each time it discoloured and the process repeated several times.

Calcium hydroxide was then used to increase the alkaline content of the water. As the paper’s fibres swelled up, brown discoloration reduced further and soluble acidity was removed during washing. The print was taken from the bath and placed on a blotting paper which additionally helped draw out some of the discoloration.

The print was washed in this manner until no further soluble discoloration could be seen. Residual staining was reduced by the application of a mild sodium borohydride bleach solution. Finally the print was placed in a bath containing calcium hydroxide, leaving an anti-acid buffer in the paper.