UPMSP Intermediate Dyeing Art flashcards

37 cards. Read the term and the definition here. The deck at the top of this page is optional.

Beer-Lambert law

States that absorbance of a dye solution is proportional to dye concentration and path length (A = εcl). Used to measure dye concentration and exhaustion colorimetrically.

Metamerism

A condition where two coloured samples appear to match under one light source but differ under another, because their spectral reflectance curves are not identical.

Kubelka-Munk equation

Relates reflectance to dye concentration: K/S = (1−R)²/2R. Higher K/S means deeper shade, and it is the basis of computer colour matching.

Subtractive colour mixing

Mixing of dyes or pigments where each absorbs part of the spectrum; the subtractive primaries are cyan, magenta and yellow, and all three together approach black.

Cotton moisture regain

Standard moisture regain of cotton is about 8%. Its many hydroxyl groups make it hydrophilic and readily dyed by reactive, vat and direct dyes.

Wool fibre chemistry

Wool is a protein (keratin) with amino and carboxyl groups, making it amphoteric. It binds acid and reactive dyes and has a moisture regain near 16%.

Polyester dyeing requirement

Polyester is hydrophobic and highly crystalline, so it needs disperse dyes applied at about 130 °C under pressure, or at lower temperature with a carrier.

Acrylic dyeing

Acrylic fibre contains anionic sulfonate sites that bind cationic (basic) dyes, giving bright shades with good light fastness on this fibre.

Reactive dye bonding

Reactive dyes form covalent bonds with cellulose hydroxyl groups, producing high wash fastness. Unfixed dye must be soaped off after dyeing.

Vat dye reduction

Vat dyes are insoluble pigments reduced by sodium hydrosulfite in alkali to a soluble leuco form, applied to the fibre, then oxidised back to pigment.

Azoic dye development

Azoic dyeing impregnates fibre with a naphthol coupling component, then develops colour by treating with a diazotised base inside the fibre.

Disperse dyes

Sparingly water-soluble dyes applied as fine dispersions, mainly to polyester and acetate. The dye dissolves into the fibre rather than binding chemically.

Acid dye application

Anionic acid dyes are applied to wool, silk and nylon from an acidic bath, where acid protonates fibre amino groups that then attract the dye.

Hank dyeing

Yarn is dyed in loose skeins hung on sticks while liquor circulates. Gentle handling suits wool and handloom yarn but the method is labour intensive.

Package dyeing

Dye liquor is pumped through yarn wound on perforated cones or cheeses. It gives uniform, level shades and suits large lots and sewing thread.

Jigger dyeing

Open-width fabric passes repeatedly through a trough between rollers. It suits woven cotton but not crease-sensitive knits, which may mark.

Winch dyeing

Fabric moves in rope form through a dye trough by a winch reel. Suitable for knits and delicate goods, but rope marks can occur.

Cold pad-batch dyeing

Reactive dye is padded onto cotton, then the fabric is rolled and stored for hours to fix. It saves salt and energy and needs no heating.

Mordant definition

A metal salt, such as alum, ferrous sulfate or stannous chloride, that forms a complex linking dye to fibre and improves fixation and fastness.

Mordanting sequences

Pre-mordanting applies mordant before dyeing, meta-mordanting applies both together, and after-mordanting treats the dyed goods. Each changes shade and fastness.

Electrolyte in dyeing

Common salt or Glauber's salt reduces the electrostatic barrier between anionic dye and cellulose, promoting exhaustion and deeper shade on cotton.

Levelling agent

An auxiliary that slows or equalises dye uptake, preventing patchy shade. Retarders and carriers act similarly for polyester and acrylic dyeing.

Bandhani resist technique

Cloth is pinched into small points and bound tightly with thread before dyeing. Untying leaves a ring of undyed dots in the dyed ground.

Batik wax resist

Melted wax is applied to cloth to block dye penetration, then the cloth is dyed and the wax removed by boiling or ironing to reveal the pattern.

Block printing paste

A thickened dye paste, made with gum or starch, is applied with carved wooden blocks. The thickener prevents the colour from bleeding beyond the design.

Indigo vat dyeing

Cloth dipped in reduced indigo leuco liquor appears yellow-green and turns blue in air as oxidation forms insoluble indigo pigment inside the fibre.

Grey scale fastness rating

Colour fastness is graded 1 to 5 against standard grey scales, one for colour change and another for staining of adjacent fabric; 5 is best.

Light fastness testing

Samples are exposed to light alongside blue wool standards graded 1 to 8, in a fadeometer or xenon arc lamp, and rated by comparison.

Crockmeter test

Rub fastness is measured by rubbing the dyed sample with white cloth, dry and wet, then grading staining. Wet rubbing is usually the weaker result.

Sublimation fastness

Resistance of disperse-dyed polyester to dye transfer as vapour at high temperature, as in heat setting or ironing. Poor fastness stains adjacent fabric.

Printing thickener role

A thickener such as sodium alginate or starch gives the print paste viscosity, holding dye in place so the design stays sharp without bleeding.

Discharge printing

A reducing or oxidising agent is printed onto dyed cloth to destroy the ground colour in patterned areas, producing white or coloured designs on a dyed ground.

Mercerisation effect

Treating cotton with strong caustic soda under tension increases lustre, strength and dye uptake, so it must be done before dyeing to avoid shade variation.

Percent on weight of fibre

Dye recipe unit, abbreviated % owf: grams of dye per 100 grams of fibre. It fixes shade depth independently of bath size.

Liquor ratio

The ratio of fibre mass to dye bath volume, for example 1:20. Changing it alters dye concentration and therefore exhaustion, levelness and shade depth.

Dyehouse PPE

Rubber gloves, goggles, apron and dust mask. Dye powders can sensitise the respiratory tract, and caustic soda and acids cause burns.

Dye powder pasting

Dye is first mixed with a little cold water into a smooth paste before dilution, preventing lumps that cause dark specks on the dyed material.