Lexitechnia

Pliny on Egyptian dyeing (Naturalis Historia 35.42):

Mirumque, cum sit unus in cortina colos, ex illo alius atque alius fit in veste accipientis medicamenti qualitate mutatus, nec postea ablui potest.

And amazingly, while there may be only one color in the vat, one color after another is made out of it in the cloth; it is changed by the quality of the chemical receiving it, and it cannot be washed out afterwards.

The technique Pliny attributes to the Egyptians is the use of mordants applied before the dyeing process to more strongly affix dye to cloth. Pliny does not use a special word for mordants; they are just colorem sorbentia medicamenta ‘color-absorbing chemicals’. Different colors are described as resulting from the process, though it is more likely different shades of the base color are being referred to.

[For qualitas.]