Color Fastness to Perspiration: Grey Scale Rating Determination for Textiles

Color fastness to perspiration, quantified through grey scale rating, is a critical quality and safety indicator for dyed and printed textiles that come into direct contact with the skin. This article explains the principle of grey scale assessment, the governing international standards such as ISO 105-E04, AATCC 15, JIS L 0848 and GB/T 3922, specimen preparation, artificial perspiration formulations, the complete testing procedure, and how test results are graded, reported and interpreted.

Technical Overview

Color fastness to perspiration is defined as the resistance of the color of a dyed, printed or otherwise finished textile to the action of human sweat. Human perspiration is a complex aqueous solution containing salts, lactic acid, urea and amino acids such as histidine, and its pH can range from weakly acidic to weakly alkaline depending on the individual, activity level and environment. When a colored garment is worn next to the skin, these constituents can swell the fiber, partially dissolve or hydrolyze dye molecules, and drive migration of unfixed dye, resulting in visible fading, shade change, or bleeding onto adjacent garments and skin.

The perspiration fastness test reproduces this exposure under controlled laboratory conditions. A specimen is soaked in an artificial perspiration solution, compressed under a defined pressure, incubated at body temperature, dried, and then evaluated. The evaluation is performed with calibrated grey scales, which convert a visual effect into a standardized numerical grade:

• Grey scale for assessing change in colour (ISO 105-A02, GB/T 250, AATCC EP 1) — used to grade fading or shade change of the specimen itself.
• Grey scale for assessing staining (ISO 105-A03, GB/T 251, AATCC EP 2) — used to grade the transfer of color onto adjacent fabric.

Both scales provide grades from 1 to 5 with intermediate half-steps (1–2, 2–3, 3–4, 4–5). Grade 5 indicates no perceptible effect, while grade 1 indicates severe change or staining. Each step of the scale corresponds to a defined colorimetric difference in CIELAB units, which makes the visual scales traceable and allows them to be replicated by instrumental measurement. Because the result directly reflects consumer experience during wear, perspiration fastness is a mandatory requirement in most national textile safety regulations and in nearly all buyer specification sheets for skin-contact products.

Testing Samples

Dyed, Printed and Finished Fabrics

Woven and knitted fabrics are the most common sample type. A specimen measuring 100 mm × 40 mm is cut, typically with the long direction parallel to the warp or wale, or at a specified bias if agreed. The specimen is placed in intimate contact with adjacent fabric to form a composite specimen. Multicolor prints, yarn-dyed checks and stripes are sampled so that all relevant colors contact the adjacent fabric; if necessary, multiple specimens are prepared.

Yarns and Loose Fibers

Yarn is knitted into a small swatch or wound tightly and uniformly onto a rigid frame or plate to produce a flat test area of the same nominal dimensions. Loose fibers are combed and compressed into a thin, homogeneous sheet mounted on a supporting backing. The prepared sheet is then treated in the same way as a fabric specimen.

Garments, Trims and Multicomponent Products

Finished garments, linings, labels, sewing threads, tapes, elastics and other components may be cut directly into specimen form. For multicomponent items such as lined jackets or quilted products, each colored layer is separated and tested either individually or in contact with the layer it touches in actual use, so that staining between components is captured.

Testing Items

A full perspiration fastness determination normally yields four independent grey scale grades:

• Color fastness to acidic perspiration — color change of the specimen (self).
• Color fastness to acidic perspiration — staining of the adjacent fabric.
• Color fastness to alkaline perspiration — color change of the specimen.
• Color fastness to alkaline perspiration — staining of the adjacent fabric.

When a multifiber adjacent fabric is used, the staining grade is assessed for every fiber stripe (for example acetate, cotton, polyamide, polyester, acrylic and wool), and the report may list each stripe individually. The lowest grade obtained under any condition is generally the governing result for conformity decisions.

Testing Methods

Applicable Standards

• ISO 105-E04 — Textiles: Tests for colour fastness, Part E04: Colour fastness to perspiration (acidic and alkaline).
• GB/T 3922 — Chinese national standard, technically aligned with ISO 105-E04.
• AATCC 15 — North American method, using an acidic perspiration solution only, incubation at 38 °C for 6 hours.
• JIS L 0848 — Japanese method for perspiration fastness.
• ISO 105-A02 / ISO 105-A03 — Grey scales for assessing change in colour and staining, respectively.
• ISO 105-A04 / ISO 105-A05 — Instrumental assessment of staining and of change in colour.

Specimen and Adjacent Fabric Preparation

The specimen (100 mm × 40 mm) is combined with either a multifiber adjacent fabric of the same size or two single-fiber adjacent fabrics, each 100 mm × 40 mm. In the two-fiber approach, one adjacent fabric is normally wool and the second is selected according to the fiber content of the specimen or the intended end use. The sandwich is stitched along one edge to maintain contact during wetting and incubation. Before testing, the composite is conditioned in a standard atmosphere as required by the method.

Artificial Perspiration Solutions

Solutions are freshly prepared with demineralized water and analytical-grade reagents. The ISO 105-E04 formulations are:

• Acid solution (pH 5.5 ± 0.2): L-histidine monohydrochloride monohydrate 0.5 g/L, sodium chloride 5 g/L, disodium hydrogen orthophosphate dodecahydrate 2.2 g/L.
• Alkaline solution (pH 8.0 ± 0.2): L-histidine monohydrochloride monohydrate 0.5 g/L, sodium chloride 5 g/L, disodium hydrogen orthophosphate dodecahydrate 5 g/L.

The pH of each solution is verified and adjusted before use. The AATCC 15 acidic solution uses a different formulation based on sodium chloride, lactic acid, disodium hydrogen phosphate and histidine monohydrochloride, adjusted to pH 4.3 ± 0.2.

Test Procedure

• Thoroughly wet the composite specimen in the test solution at a liquor ratio of 50:1 for 30 minutes at room temperature, ensuring complete penetration and squeezing occasionally.
• Remove the composite and eliminate excess liquor with glass rods or a wringer so the specimen retains the specified pick-up without free surface liquid.
• Place the composite between glass or acrylic plates in a perspirometer and apply a nominal pressure of 12.5 kPa to the composite.
• Incubate the loaded device in a ventilated oven at 37 °C ± 2 °C for 4 hours (ISO method); the AATCC method specifies 38 °C ± 1 °C for 6 hours under a 4.5 kg mass.
• Open the composite, separate the specimen and adjacent fabric, and dry them in air at a temperature not exceeding 60 °C, keeping the parts flat and undisturbed.
• Allow the dried materials to cool in a standard atmosphere before rating.

Grey Scale Rating Procedure

Visual assessment is carried out in a standardized viewing booth or color assessment cabinet under simulated daylight (typically D65) at an illuminance of at least 600 lux, surrounded by a neutral grey background. The observer views the surfaces at approximately right angles, with the light incident at about 45 degrees, and avoids casting shadows on the specimens.

• Change in colour: place the original and tested specimens side by side in the same plane, oriented in the same direction, and compare the perceived contrast with the pairs of the grey scale for change in colour (ISO 105-A02). Record the grade of the pair that shows the closest visual match.
• Staining: place the stained adjacent fabric and a clean, untreated piece of the same adjacent fabric side by side in the same plane, and compare the contrast with the grey scale for staining (ISO 105-A03). Rate each fiber stripe separately when a multifiber fabric is used.
• Half-step grades are permitted, and the original texture and orientation of the fabrics must be respected so that gloss or nap effects do not distort the judgment.

Where greater objectivity is required, the grades may be calculated instrumentally: a spectrophotometer measures the color difference between original and tested material, and ISO 105-A05 converts this into a change-in-colour grade, while ISO 105-A04 provides the corresponding calculation for staining. Instrumental results are widely accepted for arbitration and quality statistics, although visual rating remains the reference method.

Grading and Interpretation

• Grade 5 — negligible or no visible change or staining.
• Grade 4 — slight change or staining, visible only on close inspection.
• Grade 3 — visible change or staining, generally the minimum acceptance level for skin-contact textiles in most regulations.
• Grade 2 — considerable change or staining, usually rejected.
• Grade 1 — severe change or staining, clearly unacceptable.

The lower of the color-change and staining grades governs the overall result. Typical acceptance criteria include a minimum of grade 3 for adult skin-contact products under GB 18401, grade 3–4 for infant products under GB 18401 and GB 31701, and grade 3–4 or above for many eco-label and brand-specific requirements. The test report should state the method used, the pH condition, the adjacent fabric type, and all individual grades for change in colour and staining.

Applications

Grey scale rated perspiration fastness testing is applied throughout the textile supply chain:

• Sportswear, activewear and outdoor apparel, where sweat exposure during exercise is intense and prolonged.
• Underwear, socks, hosiery, swimwear and shapewear in permanent skin contact.
• Infant and children's clothing, where regulatory limits are strictest.
• Bed linens, mattress covers and furniture upholstery textiles that contact skin for long periods.
• Regulatory compliance verification for market access, including national safety codes and eco-label certifications.
• Buying-house quality control, batch release testing and supplier qualification by accredited third-party laboratories.
• Dye and auxiliary development, process optimization of soaping and fixing treatments, and root-cause analysis of customer complaints such as color bleeding onto skin or layered garments.

FAQ

What grey scale grade is considered a pass?

Most regulations and buyers require at least grade 3 for perspiration staining and color change on adult skin-contact products, grade 3–4 for infant textiles, and many premium brands specify grade 4 or higher. The applicable regulation, product class and purchase contract should always be checked, because acceptance thresholds differ between markets.

Why are both acidic and alkaline perspiration tested?

Human sweat varies in pH, and dyes respond differently to acidic and alkaline environments. A fabric may show excellent fastness in acidic solution but bleed severely in alkaline solution. The ISO and GB methods therefore test both conditions, while the AATCC method evaluates the acidic condition only.

What is the difference between color change and staining grades?

Color change describes fading or shade alteration of the specimen itself and is rated with the ISO 105-A02 scale. Staining describes the transfer of dye onto the adjacent fabric and is rated with the ISO 105-A03 scale. They are independent properties: a fabric may hardly fade yet stain heavily, so both grades must be reported.

Can grey scale rating be performed with an instrument?

Yes. Spectrophotometric measurement combined with ISO 105-A05 and ISO 105-A04 converts CIELAB color differences into equivalent grey scale grades. Instrumental rating improves repeatability and is valuable for arbitration, although standardized visual assessment in a light cabinet remains the reference procedure.

How do the ISO and AATCC perspiration methods differ?

The ISO 105-E04 and GB/T 3922 methods use histidine-based acidic and alkaline solutions, a 4-hour incubation at 37 °C and a 12.5 kPa pressure. AATCC 15 uses a single acidic solution with a different chemical formulation, incubates at 38 °C for 6 hours and applies a 4.5 kg weight. Results from the two systems are not directly interchangeable and must be attributed to the correct method.

What causes poor perspiration fastness and how can it be improved?

Common causes include insufficient washing-off of unfixed hydrolyzed dye, an unsuitable dye class for the fiber, low fixation efficiency, or inadequate after-treatment. Corrective measures include optimized dyeing recipes, thorough soaping and rinsing, application of suitable fixing agents, and selection of dyes with inherently high wet fastness. Verification through retesting by an accredited third-party laboratory is recommended after any process change.