Colourfastness to Light: Reading the AATCC 16 Scale

What Does a Colourfastness Grade Actually Describe?

The grade describes how much visible change a specimen showed after exposure, judged against a reference scale rather than by eye alone. Five represents very little change and one represents substantial change, with half steps available between them. It is a comparison against a physical reference rather than an opinion, which is precisely why it is worth specifying instead of words such as fade resistant.

How Much Exposure Does the Grade Cover?

This is the half that gets left out. Fading accumulates with exposure, so a grade earned across a short exposure says little about behaviour after months near a window. State the exposure in the units the referenced method uses, agree it with whoever will test, and write both halves on the same line. Buyers occasionally discover that a grade they were proud of was earned across something very brief.

How Do Results Compare With the ISO Route?

Two families of methods exist and both are legitimate. The route common in North American programmes works in fading units from a xenon source, while the routes published by the International Organization for Standardization work with blue wool references and a numbered scale. Neither is superior, but they are not interchangeable, so specify one and compare against the same one next season.

What Should Be Written on the Order Line?

Three items, all short: the method reference, the minimum grade, and the exposure across which that grade must hold. Add a fourth where relevant, which is the colourway this applies to, because bright and deep shades behave differently and a range-wide claim usually hides one weak colour.

Why Do Some Colours Fail Sooner Than Others?

Dyestuff chemistry decides most of it. Pale shades have less pigment to lose so small losses look larger, while deep and bright shades rely on colourants that can break down faster under light. Discharge alters the substrate itself. Because of that, a whole range rarely shares one behaviour and each important colourway deserves its own evidence.

Where Does Light Actually Reach the Product?

Three exposure paths matter and they are not equal. Retail display lighting, particularly near windows, delivers continuous exposure for months. Transport and warehouse conditions deliver less but across a longer period. And owner use outdoors or in vehicles can deliver the most intense exposure of all. Specify against whichever path your product realistically meets.

• State the grade and the exposure together, never one alone.
• Evidence each important colourway separately rather than by range.
• Ask which reference scale the laboratory used when grading.
• Consider retail window exposure where the product will be displayed.
• Record method versions so next season compares identically.
• Keep a retained coupon per colourway stored away from light.

How Is Fading Judged Objectively?

Grading compares the exposed specimen against a physical grey reference rather than asking someone to remember how the original appeared. That is why the result is repeatable between laboratories and why it can be challenged sensibly if necessary. Request that the report names the reference used, because it clarifies how the grade was reached.

What Role Do Sun and Heat Play Together?

Light rarely arrives alone. Heat accelerates the chemical change light initiates, so a bag left in a vehicle experiences both at once and fades faster than either effect alone would explain. Where outdoor storage is expected, consider that combination when setting the exposure requirement rather than testing at room conditions only.

How Do Finishes and Coatings Interact With Fading?

Surface treatments change what reaches the colourant. Ultraviolet absorbers slow the process down, while some coatings alter apparent depth and can make early change easier to see. Because of that, approving the finished cloth rather than the raw dyed material matters, and it explains why a laboratory result on unfinished fabric sometimes flatters the material.

What Does Testing Cost and How Often Is It Needed?

A single exposure run takes time, so build it into the development calendar rather than adding it at the end. Frequency depends on risk: evidence each critical colourway when it is introduced and whenever anything in the dye or finishing route changes, rather than repeating it every lot regardless of whether anything moved.

How Should a Fading Complaint Be Handled?

Start by asking what the product met, because most cases involve exposure well beyond what was specified. Compare a returned unit against a retained coupon stored dark, since that shows whether the change matches expectations for the stated exposure. Then decide commercially, with numbers rather than impressions on both sides.

How Do Reports Differ Between Providers?

Two laboratories can produce different reports for identical cloth, usually because the exposure or the reference differs rather than because either was careless. Ask what equipment was used, which version of the method was followed, and which reference was used for grading. Those three answers explain nearly every difference and tell you whether results can be compared.

What Should Be Checked Before Ordering Evidence?

Confirm the method version, the exposure, whether grading before or after any washing, and which colourways are included. Agreeing those four first prevents the common outcome where a report arrives that answers a slightly different question from the one you asked, and the whole exercise has to be repeated.

How Do Storage and Retail Conditions Compare?

Retail environments often expose goods far more than owner use does, particularly where units sit near glazing for months. Warehouse and transit add smaller amounts across long periods, and outdoor owner use delivers the most intense episodes. Set the requirement against whichever path dominates rather than against an average of all three.

How Should Brand Owners Set Requirements Internally?

Write one standard for the whole range, then note exceptions by product rather than negotiating per style. A single standard keeps buying consistent, makes supplier conversations short, and stops one weak piece carrying the reputation of everything around it. Review it annually rather than rewriting it whenever a single result disappoints.

• Ask which reference and version every provider used before comparing reports.
• Agree exposure and method before evidence is ordered rather than after.
• Evidence each critical colourway rather than one representative shade.
• Test the finished construction rather than unfinished material.
• Set requirements against the dominant exposure path realistically.
• Keep one standard per range and review it once a year.

What Does Evidence Cost, and Why Run It?

Running costs less than the complaints it prevents, and it takes calendar time rather than money. Most programmes recover the cost with the first avoided incident, particularly where several units would otherwise be replaced together. Schedule evidence early, since exposure cannot be compressed simply because shipping is close.

How Should Differences Between Lots Be Handled?

Compare physically against retained coupons first, because dye lots vary within tolerance and often explain small differences entirely. Where the gap is larger than tolerance allows, ask for the method details before drawing conclusions, then decide using both halves of the specification: the grade and the exposure it was earned across.

What Does a Well-Built Record Carry?

A good record carries the method and version, the exposure in stated units, the grade, the reference used for grading, the colourway and the lot. Six fields, one page, no adjectives. Everything a later discussion needs is present, and nothing has to be reconstructed from memory or from correspondence.

What Belongs in an Internal Standard?

A usable internal standard names the route, the minimum grade, the exposure, whether grading happens before or after washing, and which exceptions exist by product. Written once, it makes buying consistent, allows the same requirement to be quoted to every material contact, and removes the need to re-decide each season.

• Build one internal standard for the range rather than negotiating requirements style by style.
• Require method version and exposure on every report before accepting it.
• Keep six fields per record so later comparisons never depend on correspondence.
• Evidence the finished construction rather than the unfinished base material.
• Review the standard once a year rather than rewriting it after each disappointing result.
• Store retained coupons away from light for every colourway in the range.

How Should Requirements Be Communicated to Buyers Internally?

Requirements only work when everyone buying against them reads the same sentence. Put the standard in the technical file rather than in correspondence, refer to it from each development brief, and quote it verbatim when asking anyone for evidence. That habit is what turns an abstract requirement into something every shipment actually gets measured against.

How Is the Result Evidenced on Delivery?

Request the method version, the exposure amount, the grade and the colourway reference on one report tied to the lot. Then compare against retained coupons for that colourway. Where the result matters to the programme, build the requirement into purchase documents so evidence arrives before goods rather than after them.

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