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2. — At a meeting of the Photographical Section, October 
4th, 1866, it may be remembered that I exhibited some spe- 
cimens of photographs in various colours, on paper and 
calico, a process invented by Mr. John Mercer, F.RS. I 
did not recollect sufficient of what Mr. Mercer had told me 
of the process to give you any definite information as to the 
production of the colours. A few days since I stumbled on 
his description ; if it is thought of sufficient interest, please 
to communicate it to the members. 
Mr. Mercer read a paper on the subject at the meeting of 
the British Association at Leeds, in the year 1858. He ex- 
hibited coloured photographs on paper and calico, and gave 
the following directions for producing them. 
DIRECTIONS. 
34oz. of sulphate of iron are converted into peroxalate ; 
this is diluted to 2 gallons, and will impregnate 200 square 
yards of paper. The paper being floated on the solution 
until fully wet in the usual way, it is then exposed, and 
afterwards steeped in some solution which only acts on that 
part where the iron has been reduced from the per- to the 
protoxide. Red prussiate of potash and sulphuric acid act 
well, making the image blue and the ground white. 
Sulphocyanide of potassium and a salt of copper form 
another bath ; the protoxide of the picture deoxodises the 
copper, and the sulphocyanide of the suboxide of copper is 
fixed in the cambric or paper. This may be converted into 
the red prussiate of copper. 
A vast number of colours may be obtained by replacing 
the iron or copper by other metals, such as lead, zinc, tin, 
mercury, silver, gold, or manganese. 
With these bases may be used various dyes, as madder, 
cochineal, murexide, logwood, galls or quercitron bark, 
besides the iodides, chromates, prussiates, or oxides of the 
metals themselves and mixtures of these. 
