Two reason for this post. The first is just a note that Kodak, until around 1970 sold a black dye that could be used in their dye transfer process. This was also used in their Flexichrome process. It could be used to provide a quick, neutral monochromatic print using only one matrix. The color was like Medalist paper.
It was also used in derivations to provide a black line.
The second reason, was to check how long google finds this information. On Sep 29, 2015, my google search was empty of hits through the 4th page of results.
The alternate method of neutral dye was to make use of Kodak retouching color, #190-238. This isn’t sold anymore, but should you come across a supply, or formula, prepare it for use by:
an alternate method of getting to a neutral is to mix the dyes. HH Smith used to teach this method in his courses. Here is something from my notebook:
notice the use of citric acid instead of acetic acid. Henry began at a time when the DT dyeset was supplied as a powder. Citric acid works, even today…