Do Salt & Vinegar Fix Natural Dyes?

My extremely brief synopsis in the graphic below is based on my reading of the scientific literature. For the synthetic dye references, it is also based on information on the web sites of synthetic dye manufacturers. There are far more types of synthetic dyes than those shown on this graphic, but I believe that acid and fibre reactive dyes are up there in terms of popularity, which is why I included them. 

This isn't intended to educate folks on how to use synthetic dyes, but rather to demonstrate where some of the assumptions about using salt and vinegar may originate, and how newcomers to natural dyeing may mistakenly carry over those assumptions - derived from synthetic dyeing - into the craft of natural dyeing.

When it comes to table salt (sodium chloride) and natural dyes, there are many historic references to the use of 'salt' in various aspects of fibre preparation and dyeing, including references to the use of sea water. But I believe that these references predominantly relate to…

• cleaning properties of salt (i.e. when sheep are passed through salt water prior to shearing in order to kill microbes);

• a shorthand term, in old materials, for actual metal salt mordants (back in the day, the limited readership of such manuals was people working in the dye trade who understood the shorthand reference); and

• use of various salts throughout history, possibly including table salt, as a leveller (levellers slow down dye uptake, for more even dye results).