UPMSP Intermediate Dyeing Art cheat sheet

Dyeing is a transfer of dye from the bath to the fibre followed by diffusion into the fibre; equilibrium favours the fibre when substantivity is high and the bath is exhausted.

Beer-Lambert law: absorbance A = ε·c·l, so dye concentration in a solution is read colorimetrically at the wavelength of maximum absorption (λmax).

Subtractive primaries for dyes and pigments are cyan, magenta and yellow; additive primaries for light are red, green and blue.

Hue is the colour name, value/lightness is the grey level, and chroma/saturation is the purity; the three axes form the Munsell system.

Complementary colours lie opposite on the colour wheel and, mixed subtractively, give neutral grey or black rather than a bright colour.

Metamerism occurs when two samples match under one illuminant but not another; it arises because their reflectance curves differ despite equal tristimulus values.

Kubelka-Munk relation: K/S = (1−R)²/(2R), where R is reflectance at λmax; K/S rises with dye concentration and is the basis of computer colour matching.

Depth of shade depends on dye concentration on the fibre (often expressed as % owf), while brightness depends on the shape of the reflectance curve.

Cotton is cellulose with abundant hydroxyl groups: it is hydrophilic, has about 8% standard moisture regain, and is dyed with reactive, vat, direct and azoic dyes.

Wool is a protein (keratin) with amphoteric amino and carboxyl groups; it takes acid and reactive dyes and has high moisture regain (about 16%).

Silk is also protein (fibroin) but lacks wool's scale structure; it is dyed with acid, reactive and direct dyes and loses strength in hot alkali.

Polyester is hydrophobic with regain near 0.4% and a compact, crystalline structure; it needs disperse dyes and often high temperature (about 130 °C) or carrier dyeing.

Nylon (polyamide) has amide end groups that bind acid dyes; it is dyed with acid, disperse and selected reactive dyes.

Acrylic is a polyacrylonitrile fibre dyed with basic (cationic) dyes that bind to anionic sulfonate sites in the polymer.

Viscose rayon is regenerated cellulose: chemically similar to cotton but with lower crystallinity, so it absorbs dye faster and needs gentler handling when wet.

Fibre identification tests: burn test (cellulose smells of burning paper, protein of burnt hair, synthetics melt), plus solubility and stain tests.

Direct dyes are anionic, substantive to cellulose and applied from a bath with electrolyte; aftertreatment (e.g. cationic fixing agent or copper salt) improves wet fastness.

Reactive dyes form covalent bonds with cellulose hydroxyls; the reactive group is a triazine, vinyl sulfone or similar, and unfixed dye must be soaped off to reach fastness.

Vat dyes are insoluble pigments reduced in alkaline sodium hydrosulfite (hydros) to a soluble leuco form, applied to the fibre, then oxidised back to the pigment.

Acid dyes are anionic and applied to wool, silk and nylon in an acidic bath; the acid (e.g. sulfuric or formic) protonates the fibre's amino groups.

Basic (cationic) dyes are positively charged and dye acrylic, modified polyester and paper; they give bright shades but poor light fastness on protein fibres.

Disperse dyes are sparingly water-soluble, finely dispersed particles used on polyester and acetate; dyeing is by dissolution in the fibre, so high temperature or carriers aid penetration.

Azoic (naphthol) dyes are formed inside the fibre: the fibre is impregnated with a naphthol coupling component and then developed in a diazotised base, giving deep reds and maroons.

Sulfur dyes are applied from a sodium sulfide bath, reduced to a soluble form and oxidised on the fibre; they are cheap, dark-shade dyes for cotton with moderate fastness.

Hank (skein) dyeing is a batch method for yarn in loose loops; the yarn is hung on sticks and the liquor circulated or the hanks moved, giving gentle handling for wool and handloom yarn.

Package dyeing forces dye liquor through yarn wound on a perforated cone or cheese; it gives level, uniform results and is suited to large lots and sewing thread.

Jigger dyeing passes open-width fabric repeatedly through a trough between two rollers; it suits woven cotton and low-tension fabrics but not crease-sensitive knits.

Winch (beck) dyeing circulates fabric in rope form through a trough; it handles knits and delicate fabrics but can cause rope marks and lengthwise tension.

Pad-dry-cure and pad-batch methods impregnate fabric with dye by padding (wet pick-up usually 60-80%), then fix by heat or by batching at room temperature.

Exhaust dyeing relies on gradual dye transfer from a finite bath; levelness is controlled by temperature rise, electrolyte addition and pH.

Jet dyeing machines move fabric with a liquor jet in a closed vessel, giving short liquor ratios and low water use compared with winches.

Cold pad-batch suits reactive dyes on cotton: pad, roll and store for several hours, then wash off, avoiding salt and saving energy.

A mordant is a metal salt that forms a coordination complex bridging dye and fibre; common mordants are alum (potassium aluminium sulfate), ferrous sulfate and stannous chloride.

Mordanting can be pre-mordant (mordant first), meta-mordant (simultaneous) or after-mordant (mordant after dyeing); the order changes shade and fastness.

Alum generally brightens and gives good light fastness; iron (ferrous) saddens and darkens shades; tin brightens but can make wool harsh and brittle.

Tannic acid followed by tartar emetic is a traditional mordant route for cotton, which lacks the ionic sites that wool has.

Electrolyte (common salt or Glauber's salt) promotes exhaustion of anionic dyes on cellulose by reducing the negative charge barrier between dye and fibre.

Alkali (soda ash, caustic soda) controls pH: it fixes reactive dyes on cellulose and is essential for vat reduction, but excess alkali damages wool.

Levelling agents and retarders slow dye uptake to prevent uneven shade; carriers (e.g. o-phenylphenol) swell polyester for disperse dyeing at lower temperature.

Sequestering agents (EDTA, polyphosphates) tie up calcium and iron in hard water, preventing precipitation, dull shades and spots.

Bandhani is resist tie-dyeing: cloth is pinched and bound tightly with thread into small knots before dyeing, leaving undyed dots when untied.

Batik uses melted wax as a resist; wax is applied with a brush or tjanting, the cloth dyed, and the wax removed by boiling or ironing.

Tie-dye (leheriya, shibori, clamp resist) works by folding, binding or clamping cloth so that dye cannot reach the compressed areas.

Block printing applies dye paste to cloth with carved wooden blocks; the paste is a thickener (gum or starch) plus dye, not a simple solution.

In bandhani and batik, the sequence of dyeing runs from light to dark, so the deepest shade is applied last.

Traditional mordant-and-dye work on handloom cotton often uses natural dyes such as madder (alizarin) for red, indigo for blue and pomegranate rind for yellow.

Indigo is a vat dye: the cloth is dipped in reduced yellow-green leuco liquor and turns blue on exposure to air as it oxidises.

Handloom goods are usually dyed in hank or open-width form at low tension; shrinkage and warp distortion must be checked before and after dyeing.

Colour fastness is the resistance of a dyed material to change (fading) and to staining of adjacent undyed fabric; it is graded on a 1-5 grey scale (5 best).

Wash fastness is tested by laundering the sample with adjacent multifibre or single-fibre strips, then assessing change and staining against grey scales.

Light fastness is tested by exposing samples alongside blue wool standards (1-8, 8 best) in a fadeometer or xenon lamp.

Rub fastness (crocking) is tested dry and wet with a crockmeter; reactive and vat dyes generally score well, direct dyes poorly when wet.

Perspiration fastness uses acidic and alkaline artificial perspiration solutions, important for skin-contact garments.

Sublimation fastness is critical for disperse-dyed polyester; poor sublimation fastness transfers dye onto adjacent fabric during heat setting or ironing.

Quality control checks include shade matching (spectrophotometer or visual against a standard), pH of the dyed fabric, and residual unfixed dye after soaping.

Fastness ratings are compared with standard grey scales: one scale for colour change, a separate scale for staining.

Printing is localised dyeing: a thickener (sodium alginate, starch, gum) holds the dye paste so it does not bleed beyond the design.

Reactive printing on cotton uses an alkali in the paste and steam fixation, then washing to remove thickener and unfixed dye.

Pigment printing uses a binder that adheres pigment to the surface; it works on any fibre but gives stiffer handle and lower rub fastness.

Discharge printing removes dye from a dyed ground with a reducing agent printed into the cloth; resist printing prints a paste that blocks later dyeing.

After-printing processes include steaming (fixation), washing-off and soaping, which develop colour and improve fastness.

Finishing operations on dyed goods: stentering for width and straightening, calendering for lustre, sanforising for shrinkage control.

Mercerisation of cotton with strong caustic soda increases lustre, strength and dye uptake, so it changes shade depth and must precede dyeing.

Soaping after dyeing removes unfixed dye and thickener and is essential for good wash and rub fastness.

Common dyehouse tools: stainless steel dye pots (iron and copper react with dyes), measuring cylinders, thermometers, pH papers/meters, balance and stirring rods.

Weighing is the basis of recipe accuracy: dye is calculated as % owf (grams dye per 100 g fibre), so an inaccurate balance directly changes shade.

Personal protective equipment for dyeing includes rubber gloves, goggles, apron and mask; many dye powders are respiratory sensitisers.

Caustic soda and concentrated acids are handled with eye protection and added slowly to water (never water to acid) to control heat.

Sodium hydrosulfite and other reducing agents must be stored away from heat and moisture and used with ventilation, as they release sulfur dioxide.

Dye powders should be pasted with a little cold water before dilution to avoid lumps that cause specking on the fabric.

Liquor ratio (e.g. 1:20) is fibre mass to bath volume; changing it alters dye concentration and therefore shade and exhaustion.

Spills of dye powder are cleaned dry first, then wet, and drains should not receive concentrated dye liquor without treatment.