THE first photographic mordant dye process to attract attention was the silver-iodide pro.cess of Dr. Traube (U. S. Pat. 1,o93,5o3, I914). Metallic silver photographic images converted to silver iodide and immersed in solutions o.f basic dyes. become strongly co.lored. If the dye is then fixed by tannin, the silveriodide can be dissolved o.ut, leaving a transparent dye image. Traube's method was inaproved upon by Tauleigne and Mazo (U. S. Pat. I, O59,917, 1913) , who sh.o.wed how to produce a silver-iodide image having a stronger affinity for the basic dyes, and incidentally that by first hardening the gelatine with alum and ~hen treating the silver-iodide image with a strong solution of potassium ~odide it was made so transparent that for most purpo.ses it was unnecessary to dissolve out the silver-iodide image. The step of hardening the gelatine in alum to prevent it from softening and dissolving .in the strong potassium iodide solution was omitted in the Un.ited States patent specifications, but was published in the British Journal Photographic Almanac, 1912 , page 653. Hoyt Miller (U. S. Pat. 1,214,94o,,I917), as a result of experiments with the process without alum hardening, declared the process unwo,rkable, and broadly claimed the production and dyeing of a transparent silver-iodide image, he: hardening the g'el~fine with formalin. I ~have myself operated the Tauleigne-Mazo process with perfect success.
Incidentally it had beerl discovered that silver ferrocyanide, silver chromate and .some other silver salts could be similarly dyed, but not with satisfactory results. Fox (U. S. Pat. I,I66,-123, I916), disclo.sed the fact that a vanadium-toned .silver image mordanted basic dyes, and Crabtree and Ives (priority :to Crabtree.) independently discovered that a copper-toned image had the same property to a very notable and useful degree. The copper-toned image, like the ~transparent kind of silver-iodide image, is sufficiently transparent for most purposes without" fixing out," * Communicated by the Laboratories.