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Scope and Purpose
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In the world of textile quality control, the assessment of colourfastness is a fundamental requirement for ensuring product quality and customer satisfaction. The standard CAN/CGSB-4.2 No. 5.2-M87 (2013) — officially titled Textile Test Methods — Colourfastness Tests — Grey Scale for Assessing Change in Colour — serves as the cornerstone of colourfastness evaluation in Canada. This standard is technically identical to the widely recognized ISO 105-A02 standard, providing a harmonized method for determining how much a textile specimen has changed in colour after exposure to a test agent such as light, washing, or perspiration.
This article provides a comprehensive technical overview of the standard, covering its scope, precise technical specifications, practical implementation, and compliance requirements for textile testing laboratories and quality assurance professionals.
Scope and Purpose
The scope of the standard is precisely defined: it specifies a grey scale and describes its use for assessing the change in colour of textiles in colourfastness tests. The grey scale provides a visual reference against which the perceived colour difference between an untreated (original) specimen and a treated (tested) specimen is compared and rated.
The standard is designed to be universally applicable across all colourfastness procedures specified in the CAN/CGSB-4.2 series. Whether testing for wash fastness, light fastness, crocking, or perspiration fastness, the grey scale for assessing change in colour provides the final metric of performance. The core principle is simple: the user compares the contrast observed in the test specimen to the graduated contrasts of the grey scale, which range from Grade 5 (negligible or no change) to Grade 1 (severe change).
Harmonized Framework: Because CAN/CGSB-4.2 No. 5.2 is fully aligned with ISO 105-A02, textile manufacturers who export globally can confidently use this standard without needing to duplicate testing procedures for different markets. This simplifies quality assurance programs and reduces the cost of compliance.
Technical Specifications and Colorimetric Requirements
The authority of the grey scale test lies entirely in the precise colorimetric properties of the scale itself. The standard defines a grey scale consisting of nine pairs of grey plastic chips. One chip in each pair is a uniform neutral grey (the reference colour). The second chip in each pair represents the simulated “change” in colour. The contrast between the two zones of each pair corresponds to a specific visual colour difference known as a colour tolerance.
The physical scales must be manufactured to tight colorimetric tolerances measured under standard CIE D65 illumination. The pairs correspond to the following full and half-grades:
Table: Colorimetric Specifications for Grey Scale Grades
| Grade | CIELAB Colour Difference ΔE*Lab | CIELAB Tolerance |
|---|---|---|
| 5 | 0.0 | ± 0.2 |
| 4-5 | 0.8 | ± 0.2 |
| 4 | 1.7 | ± 0.3 |
| 3-4 | 2.5 | ± 0.3 |
| 3 | 3.4 | ± 0.4 |
| 2-3 | 4.8 | ± 0.5 |
| 2 | 6.8 | ± 0.6 |
| 1-2 | 9.6 | ± 0.7 |
| 1 | 13.6 | ± 1.0 |
The table explicitly shows that the relationship between visual grade and colour difference is geometric, not linear. This was carefully defined to match the sensitivity of the human eye across the entire range of colour change. The L* values of the grey chips are also strictly controlled to ensure the scale remains neutral and does not drift in hue or lightness over time.
Implementation Highlights and Testing Procedure
Proper implementation of the standard involves strict adherence to the viewing and assessment conditions. The test specimen and the grey scale must be illuminated by a standard daylight source (D65) using a 45/0 or 0/45 geometry at a defined distance (typically 30 cm). The observer must look at the plane of the specimen at an angle of approximately 90 degrees.
Pro Tip for Technicians: To avoid fatigue, limit continuous grey scale assessment sessions to 30 minutes. If visual judgment becomes difficult, use a mask with a window cut out to isolate the specific areas being compared. This prevents surrounding colours from influencing the perception of contrast.
The standard samples are mounted side-by-side in the same plane. The original and the test specimen are placed adjacent to each other, and their contrast is compared directly to the contrasts of the grey scale. The grading is determined by selecting the grey scale pair that best represents the visual contrast observed in the specimens.
Caution on Metamerism: When assessing colour change, be aware of metameric failure. If the original and test specimen match perfectly under the lab light source (D65) but appear different under other light sources, the data may be misleading. This standard assumes assessment under a specific light source, and conditions outside this specific setting are not covered by the standard’s scope.
Compliance Notes and Quality Control
Compliance with CAN/CGSB-4.2 No. 5.2-M87 (2013) is not merely about owning a grey scale. It requires a rigorous quality management system for the scale itself and the specimen preparation. Laboratories seeking accreditation (e.g., ISO 17025) must demonstrate proficiency in using this standard.
Scale Verification and Calibration: The standard mandates that the grey scale used in testing must be checked at regular intervals against a primary reference scale that meets the colorimetric values specified in the table above. A spectrophotometric check must confirm that the CIELAB colour difference values remain within their specified tolerances.
Critical Compliance Failure: A common audit finding is the use of a grey scale that is physically damaged, dirty, or faded. A scale that no longer meets the strict CIELAB tolerances will produce invalid results. Laboratories must maintain records of scale verification and clearly log the date of first use and scheduled retirement of each physical scale.
The standard has been reaffirmed in 2013, confirming its continued relevance. Since it is an adoption of ISO 105-A02, any updates to the international standard are typically reviewed for potential adoption into the CGSB framework. This ensures Canadian testing remains globally competitive and accepted.
Frequently Asked Questions
Q: What is the fundamental difference between CAN/CGSB-4.2 No. 5.2-M87 and the AATCC Grey Scale for Color Change (EP 1)?
A: Historically, the scales had different tolerances. However, modern practice has seen these standards harmonized very closely. CAN/CGSB-4.2 No. 5.2 is an identical twin of ISO 105-A02, while AATCC EP 1 is its own standard. For practical purposes, the same physical scale can often be used for both, but the specific contractual requirements of the buyer dictate which standard is legally applicable. In Canada, CAN/CGSB is the mandatory standard for government procurement and domestic testing compliance.
A: Historically, the scales had different tolerances. However, modern practice has seen these standards harmonized very closely. CAN/CGSB-4.2 No. 5.2 is an identical twin of ISO 105-A02, while AATCC EP 1 is its own standard. For practical purposes, the same physical scale can often be used for both, but the specific contractual requirements of the buyer dictate which standard is legally applicable. In Canada, CAN/CGSB is the mandatory standard for government procurement and domestic testing compliance.
Q: My laboratory uses instrumental measurement. Can we bypass the visual grey scale?
A: No. The visual grey scale is the referee method. Instrumental methods (such as those in CAN/CGSB 4.2 No. 88 or ISO 105-J05) must be calibrated against the visual grey scale to ensure that an instrumental pass/fail matches a visual pass/fail. While instrumental assessment is faster and removes human bias, the grey scale remains the ultimate standard against which all decisions are traced back.
A: No. The visual grey scale is the referee method. Instrumental methods (such as those in CAN/CGSB 4.2 No. 88 or ISO 105-J05) must be calibrated against the visual grey scale to ensure that an instrumental pass/fail matches a visual pass/fail. While instrumental assessment is faster and removes human bias, the grey scale remains the ultimate standard against which all decisions are traced back.
Q: How is the “Change in Colour” strictly defined in this standard?
A: The standard defines the change in colour as the total perceived difference in lightness, hue, and chroma between the original and the test specimen. It encompasses any alteration in the characteristics of colour. The grey scale assesses this total combined contrast. It does not separate staining from colour change, which is covered by a separate grey scale (for assessing staining) defined in CAN/CGSB-4.2 No. 5.3.
A: The standard defines the change in colour as the total perceived difference in lightness, hue, and chroma between the original and the test specimen. It encompasses any alteration in the characteristics of colour. The grey scale assesses this total combined contrast. It does not separate staining from colour change, which is covered by a separate grey scale (for assessing staining) defined in CAN/CGSB-4.2 No. 5.3.
In conclusion, CAN/CGSB-4.2 No. 5.2-M87 (2013) represents a mature, scientifically robust, and globally harmonized standard for evaluating textile colourfastness. Its reliance on precise colorimetry and controlled visual analysis ensures that a “Grade 4” in a laboratory in Toronto is exactly the same as a “Grade 4” in a lab in Berlin. Adherence to this standard is essential for any organization looking to certify the quality and durability of its textile products within the Canadian market and beyond.
Technical article published 2026. Always verify the latest reaffirmation date for the most current regulatory status.
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