D y e i n g ,   p r i n t i n g ,   f i n i s h i n g

In finished fabrics, a distinction is made between yarn-dyed and piece-dyed fabrics. In the first instance, the yarn is degummed, dyed and twisted before weaving. This is the case of taffetas, duchess satin, jacquard weaves etc. In the second case, the fabric is woven and degummed before being dyed, e.g. crepes, twills etc. Whether at the yarn stage of the fabric stage, degumming is required to remove the sericin which accounts for up to 25% of the weight. This weight-loss had to be made up for by adding a chemical or mineral substance. Nowadays the recovery of the weight-loss is often achieved by chemically ‘grafting’ a monomer onto the silk polymer.

Dyeing.

Before about 1815-1830, piece dyeing was practically unknown. The commonest form of dyeing consisted of soaking the raw-silk skeins in tanks of dyestuffs. Piece-dyeing was introduced in Lyon and became industrialised around 1849. For a long time, it remained a speciality of the Lyon region. There are several different processes of piece-dyeng. The fabric can be fed into a dye-bath through two cylinders, or it can be fixed to a jig which is immersed in the dye-bath. While the fabric is attached to the jig, the dyestuff is fixed then the fabric is rinsed and dried.

Printing.

Printing is a form of localised dyeing, i.e. a pattern or motif is placed at specific points on the fabric. There are several printing techniques, the most commonly-used being :

Roller-printing : This method was invented in 1785 by a Scot, Bell. The fabric is printed mechanically by passing through two rollers which have been engraved with the required design. This method is ideally suited to very long runs and consequently is not used very much for silk fabrics.

 Screen-printing : This is an ancient method of printing, which was industrialised in Lyon around 1850 hence its name ‘à la lyonnaise’

 Finishing. With the exception of pattern weaves, all fabrics have to be finished. It is the finisher who gives satin its shimmering suppleness and its ‘hand’. Finishing gives a fabric the desired appearance and feel. There are numerous finishing treatments, both physical and chemical, designed to ensure crease-proofing, water-proofing, flame-retardance etc.