What is the purpose of dipping the shirt in vinegar at the end of the process?

One can use any sort of fiber in dyeing, if the correct dye is chosen. Different fibers require different types of dye.

There is no purpose to dipping a shirt in vinegar at the end of the dyeing process, unless the shirt is made of silk and will benefit from correcting its pH.

These questions are answered on various pages on my web site. Please read before sending questions.