Pyrogallic acid . 8o „ 8 „ Potassium metabi sulphite . . 8ck „ 8 fl Boric acid (crystals) io „ I „ Water . . . zo oz. i,000 ccs.
B. Sodium sulphite . I „ 5o g.
Sodium carbonate I „ 5o „ Water . . . 20 „ i,000 ccs.
The boric acid is used as a restrainer because of its remarkable corrective power in cases of over exposure.
A mixture of hydroquinone and eikonogen was introduced in 1892 under the name of " Mixtol." The formula is : Sodium sulphite . 924 grs. 92 g.
Hydroquinone . . 115 „ II .5 „ Eikonogen . . • 77 „ 7'7 11 Potass. ferricyanide • ,, ,, Potassium carbonate . 577 „ 57'7 ,, Caustic potash . . 115 „ r1.5 „ Potassium bromide . 8 „ •8 „ Boiling water . . 18 oz. 1,000 ccs.
Glycerine to . . 5 mins. 5 Mix in the order named, allowing each to dis solve before adding the next. The solution is of CI yellowish colour, and keeps well. For " instantaneous " work, add one-half water ; for time exposures, two-thirds, or omit the caustic potash and increase the carbonate to 70o grs., and add more bromide if necessary. It may be used over and over again, and it is claimed not to stain or frill.
A mixture of rodinal, hydroquinone, and eikonogen, known as " Cydol," was at one time popular. The formula is : Eikonogen . . Ioo grs. I° g.
Hydroquinone . . 3o „ 3 ,, Rodinal . . . 9 drms. '9 „ Sodium sulphite . 24 oz. 125 „ Potassium carbonate . „ 125 „ Water to . . 20 „ 1,000 CCS.
The above is a stock solution. For use in warm weather, I part is mixed with 7 parts of water ; in cold weather, less water is used ; and in very cold weather, only 3 parts of water.
Two developers are sometimes used separately instead of mixing, but they have no advantages over the combined developers given above. Detail is first secured with a quick-working developer and density afterwards obtained with a slower-working one. The following is an example : Develop with rodinal of ordinary developing strength until all detail has been brought out ; then finish with ordinary pyro soda developer, or preferably with the following one-solution mixture of hydroquinone : Hydroquinone . . izo grs. 12 g.
Sodium sulphite . 1 oz. ,, Potassium carbonate . if „ 83 „ Water to . . 20 „ i,000 ccs.