En köpares verkliga fråga om färg är kort. När kunden tvättar detta, kommer det att springa på hennes vita handduk? Kommer det att blekna? Och vad ska jag skriva in i specifikationen så att det inte händer?
Svaret är satt långt innan plagget sys. Den sätts av fibern, av den färgämnesklass som valts för den fibern, och hur noggrant överskottsfärgen tvättades ut efteråt. Allt annat är detaljer.
Fiber avgör vilket färgämne som kan användas
Ett färgämne måste ha något att hålla fast vid. Olika fibrer erbjuder helt olika kemi, vilket är anledningen till att ett färgämne inte kan tjäna dem alla.
- Cellulosafibrer — bomull, linne, viskos. Fibern bär hydroxylgrupper. Dessa kan fås att reagera kemiskt med ett färgämne, vilket är grunden för bästa tvättäkthet som finns på bomull.
- Proteinfibrer — siden och ull. Dessa bär amino- och karboxylgrupper, så de beter sig som ett milt syra-bassystem. De tar sura färgämnen, som huvudsakligen hålls av jonisk attraktion.
- Polyester — har nästan inga färgställen alls och stöter bort vatten. Den är färgad med dispergerade färgämnen, som trycks in i polymeren vid hög temperatur och sedan fysiskt fångas där när den svalnar.
Det är därför ett bomullsfärgämne inte färgar polyester, och en sidenfärg kommer inte att färga bomull ordentligt. Det är också roten till de flesta blandningsproblem, längre ner.
Färgklass avgör hur bra färgen håller
Inuti en fiber, valet av färgämnesklass är den enskilt största spaken för beständighet.
På bomull, linne och viskos
Reaktiva färgämnen bildar en kovalent bindning med fibern. Färgen blir en del av fibern, inte en passagerare på den. Rätt applicerad och ordentligt tvättad, this gives very good wash fastness, and it is the normal choice for a garment expected to survive repeated home laundering.
Direct dyes are simpler and cheaper to apply, but they are only held by weak physical forces. Water-soluble dye sitting on the fibre surface is removed by repeated washing, so colour loss is expected rather than accidental. Direct dyeing is not the right choice for a shade you need to hold.
Vat dyes are insoluble. They are chemically reduced into a soluble form, absorbed, then oxidised back to the insoluble form inside the fibre, where they are effectively stuck. Wash and light fastness are generally strong.
Indigo is the well-known exception in that family. The molecule is large and stays near the yarn surface — the core of the yarn is left white. Det ytskiktet är anledningen till att indigo gnider av, och det är en egenskap hos färgningsmetoden, inte ett fel i en viss sats.
På siden och ull
Syra färgämnen täcker ett enormt utbud. Vissa är utmärkta, vissa är fattiga, och löslighet är en ganska grov guide: ett mycket vattenlösligt surt färgämne tenderar att fortsätta lämna med vattnet. Särskilt siden kan se fantastiskt ut på galgen och göra dig besviken efter tvätt, eftersom bindningen är en attraktion snarare än en kemisk reaktion. Våtfasthet på siden förtjänar särskild uppmärksamhet, inte ett antagande.
Pigment, som inte är färgämnen
Ett pigment har ingen affinitet för någon fiber. Den limmas på ytan av en bindemedelsfilm. Det är en verklig och användbar teknik, men det har en förutsägbar konsekvens: det som sitter på ytan kan gnidas av ytan. Pigmentfärgen knäcker mer än färgad färg, och ju djupare nyansen desto tjockare pigmentlagret.
Ofixerad färg är anledningen till att den första tvätten blöder
Ingen färgning fixar helt. Vid reaktiv färgning, en del av färgämnet reagerar med vatten istället för med bomullen. Det hydrolyserade färgämnet är färgat, det sitter fast i tyget, och den är inte bunden till någonting. Det kommer ut — frågan är bara om det kommer ut på färgeriet eller i kundens maskin.
Att ta bort det är sköljnings- och tvålningsstegen efter färgning. Det tar flera sköljningar, några av dem varma, eftersom borttagningshastigheten ökar med temperaturen. Att klippa det steget kort är osynligt på nyanskortet och uppenbart vid första tvätten.
Alltså när ett plagg blöder kraftigt en gång och sedan beter sig, det är nästan alltid överskott av ofixerat färgämne, inte en fel färgämnesklass. When it keeps bleeding wash after wash, the dye class or the fibre match is wrong.
Where blends and multi-colour pieces go wrong
A cotton and silk blend needs two dye chemistries in one fabric — one for the cellulose, one for the protein. Each is applied under conditions the other does not like. The usual approach is sequential: dye one component, then the other.
The risk is cross-staining. The cotton dye deposits on the silk, or the silk dye on the cotton, where it has no proper bond. It looks like colour. It behaves like surplus dye. Union shades on blends should be judged on wet fastness, not only on whether the two fibres match in tone.
The same logic applies inside a single piece. A print with a white ground beside a deep navy, a kaftande with a white body and a dark contrast band, a scarf with a pale border — every one of these puts loose dye next to a surface that shows it. The failure is not that the navy fades. It is that the white goes grey-blue.
Anything sewn from more than one colour deserves the same question: what happens when these two are wet together?
Rubbing is the failure your customer will actually complain about
Colour transferring by rubbing is called crocking. It is tested dry and wet, and wet is always the harder result.
This is the complaint that reaches a brand’s customer service desk. Dark trousers on a light sofa. A deep-dyed bag against a white shirt. A kaftan marking the wearer’s skin at the neckline in hot weather. None of these involves a washing machine at all.
Two things make crocking worse, both predictable:
- Depth of shade. A deep colour needs more colourant, and more of it ends up near the surface. Black, navy and deep maroon are the usual offenders.
- Colour that sits on the surface by design. Pigment prints and indigo both do this.
A deep pigment print is therefore the hardest case in the range, and it is worth agreeing a realistic wet rub expectation for it in advance rather than discovering the number after production.
The shades that are hardest to hold
Shade matters as much as fibre. Deep navy, black and deep red need heavy dye loading, so surplus dye and surface dye are both higher, and both wash and rub results tend to fall. Indigo rubs by nature. Turmeric is worth naming because it looks so convincing and lasts so poorly — curcumin sits on the fibre rather than bonding into it, and it is very sensitive to light. A turmeric yellow can visibly dull after a short period outdoors.
Pale and mid shades are easier on every count.
Mercerisation, and why it helps the colour
Mercerisation treats cotton with caustic soda. The fibre swells permanently, and its cross-section changes from a flat, twisted ribbon to something rounder and smoother. Two things follow.
More of the fibre becomes accessible to dye, so uptake improves markedly. A given depth of shade can then be reached with less dye — which is helpful for fastness, because less dye means less surplus to wash out. Deep shades also become easier to reach at all.
Andra, if the fabric is held under tension during the treatment, the smoother surface reflects light more evenly and the fabric gains lustre. Mercerised cotton simply looks richer in a deep shade.
How colour is tested, and how results are graded
The main international methods sit in the ISO 105 series. Name the part, not just “colour fastness”.
Tvätt
ISO 105-C06 covers colour fastness to domestic and commercial laundering, using a reference detergent. The specimen is laundered with specified adjacent fabrics under set conditions of temperature, alkalinity and abrasive action. It offers single and multiple test variants, so the conditions must be named — a result is meaningless without them. ISO 105-C10 is the older washing method using soap, or soap and soda. In the American system, AATCC TM61 is the accelerated laundering method.
Rubbing
ISO 105-X12 is colour fastness to rubbing. A standard white cotton cloth is rubbed against the specimen on a crockmeter, dry in one test and wet in another, and the staining on the white cloth is graded. AATCC TM8 is the equivalent crocking method; AATCC TM116 uses a rotary vertical crockmeter, which is designed for testing areas too small for the standard instrument — useful on a small print motif.
Light and perspiration
ISO 105-B02 assesses fastness to artificial light using a xenon arc lamp. ISO 105-E04 covers perspiration, in both acid and alkaline form, which matters for anything worn against the skin in heat.
Reading the grades
Results are read against grey scales, and this is the part worth understanding properly, because two different things are graded separately.
- Change in colour — has the specimen itself shifted? Graded on the grey scale of ISO 105-A02, från 5 for no change down to 1 for severe change, with half steps between.
- Staining — has colour transferred onto the white fabric beside it? Graded on the grey scale of ISO 105-A03, again from 5 for no staining down to 1, with half steps.
A single number on a report is therefore incomplete. Ask which one it is.
Staining is usually reported against a multifibre adjacent fabric, specified in ISO 105-F10. This is a woven strip containing several different fibres in bands — bomull, polyester, polyamide, akryl, wool or viscose, and an acetate — so one test shows which fibres the dye stains. That detail is directly useful: a dye that stains the polyamide band tells you what will happen to a nylon lining or a swim garment packed next to it.
Light fastness is graded on a different scale entirely. It uses blue wool references numbered one to eight, where each step is roughly a doubling of resistance. Do not compare a light fastness number with a wash fastness grade; they are not the same scale.
What the end consumer does to the garment
Laboratory conditions are controlled. Households are not, and the difference explains a share of complaints.
- Wash temperature. Hotter water removes more colour and moves it around more freely. The same garment that is stable in cool water can release dye in a hot wash.
- Hard water. Calcium and magnesium interfere with detergents and with the agents meant to protect colour, and can leave deposits that dull a shade. Buyers selling into hard-water regions see more colour complaints for the same goods.
- Detergent choice. Detergents formulated for whites commonly contain optical brighteners. They are intended to make white look whiter and are not made for coloured garments; over many washes they work against the appearance of a deep shade.
- Drying in sunlight. Direct sun is a fading exposure. A light-sensitive dye can lose noticeable brightness quickly this way, and consumers in hot countries dry outdoors as a matter of course.
None of this changes the chemistry of the dye. It changes how much of that chemistry the customer gets to see.
What to write into your specification
Vague requirements produce vague results. These are the points buyers commonly agree with a supplier before bulk, and each one closes a specific gap.
- Name the test method and its part. “Good colour fastness” är inte en specifikation. “ISO 105-C06” är, and so is naming the conditions — temperature, and single or multiple test.
- Ask for shade change and staining as separate grades. A report giving only one figure is telling you half the story.
- Ask for the staining result across the multifibre bands, not as a single averaged number.
- Ask for dry and wet rubbing separately. The wet result is the one that predicts a complaint.
- Set expectations shade by shade, not one figure for the whole range. A pale print and a deep navy will not deliver the same grade, and a blanket requirement written for the pale shade will be missed by the navy. What is realistic depends on the shade, the dye class and how the garment is used — a scarf worn against a coat is a different case from a lined jacket.
- Specify the tested shade explicitly. A result on a standard shade is not a result on your colour. Deep shades in particular need testing on the actual production shade.
- For any piece with a white or pale ground next to a deep colour, call it out. Ask specifically for staining onto the light ground.
- For blends, ask how the two fibres were dyed, and treat wet fastness as the acceptance point rather than shade matching alone.
- For skin-contact garments and anything for warm markets, add perspiration to the list.
- For prints and deep bag or trim colours, treat rub fastness as the primary criterion, not a secondary check.
The useful habit is to think about the failure before the fabric exists. Ask what the customer will put this garment next to, våt, and specify the test that answers that question.
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