At all times have the feathers, which are to be dyed, scoured well, that is, washed clean from all externally adhering impurities, fat, etc.; naturally colored feathers bleached for all light and medium shades to be dyed upon them, and rinsed perfectly clean from the scouring or bleaching bath, first in two or three warm waters and then in cold water.
On taking the feathers from any bath, always squeeze the liquid out first by drawing the feathers through the hand closed upon them, then by placing them straight between several laps of clean dry muslin and repeatedly passing the hand with quite a smart pressure over it. Never transfer the feathers, in any case, from one bath to another in a wet, but in a moist condition, or nearly dry.
Never allow the feathers to become dry in the course of operations. If it is necessary to interrupt work, or to put feathers to one side for further treatment, dry them properly by first passing them through a bath of raw starch, in order to have the flues at all times as well opened as possible.
In no case let the temperature of a bath, in which feathers are treated, rise to actual boiling, although for some dyestuffs a temperature near the boiling point is required to make them dye up, to become level or to fix them.
In every instance, where an acid or acid salt is employed, either in a separate mordanting or fixing bath, or as a component of the dyebath, rinse well before drying.
When sulphuric acid is used in the composition of a bath, add only so much of it as to give the water a very slight, scarcely perceptible acid taste.
Although some artificial dyestuffs dye up without an addition of acid to the dye bath (basic dyestuffs), the addition of sulphuric acid, in a very small quantity, to the dye-bath is advantageous, rendering the colors brighter and also faster.
When bisulphate of soda is employed, it is not necessary to also add sulphuric acid to the dye-bath; if it is added, however, it must only be in a very small quantity; careful rinsing in several warm and cold waters after dyeing is required.
When alum alone is used without any other addition as mordant, sulphuric acid may be added, but only in the proportion of one tenth or, at the most, up to one fifth of the weight of alum, and careful rinsing in several warm and cold waters is the more indispensably required the more acid has been employed.