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CAN CGSB 4.2 No. 27.6-2015: Standard Test Method for Colour Fastness to Rubbing (Crocking)
A comprehensive guide to the Canadian standard for evaluating colour transfer from textiles via rubbing
Scope and Purpose
CAN CGSB 4.2 No. 27.6-2015 is a nationally recognized test method within the CAN/CGSB-4.2 series of textile test standards. It specifies a procedure for determining the resistance of colour in textile materials of all kinds, including fibres, yarns, and fabrics, to rubbing off and staining other surfaces. The method simulates the mechanical action of rubbing through both dry and wet procedures, providing a reliable assessment of colour fastness to crocking. This standard is essential for quality control in textile manufacturing, apparel production, and international trade, as poor crocking fastness can lead to consumer complaints and product returns.
The standard applies to textiles made from natural, synthetic, or blended fibres, and is applicable to dyed, printed, or otherwise coloured materials. It does not cover pile fabrics or carpets, which are addressed by other test methods. Two distinct test conditions are defined: a dry rub test and a wet rub test, each using a standardized crockmeter and a specified white rubbing cloth.
Tip: For best reproducibility, ensure the crockmeter is calibrated regularly and the rubbing cloth meets the specifications of CAN/CGSB-4.2 No. 27.6-2015 regarding fibre composition, weight, and finish.
Technical Requirements
Apparatus and Materials
The test requires a motorized or manual crockmeter that provides a consistent linear stroke of 104 mm at a speed of one cycle per second. The rubbing finger (or peg) has a flat, circular face with a diameter of 16 mm, exerting a force of 9 N ± 0.2 N. The standard rubbing cloth is a desized, bleached, mercerized, and unfinished cotton fabric with a specified weight (between 100 and 130 g/m²) and a white reflectance of at least 85%.
Test Specimens and Conditioning
Specimens are cut to a minimum size of 50 mm × 140 mm, with the longer dimension parallel to either the warp or weft direction depending on the intended end‑use. All specimens must be conditioned at 21 °C ± 1 °C and 65 % ± 2 % relative humidity for at least 4 hours prior to testing. For the wet rub test, the rubbing cloth is thoroughly wetted with distilled or deionized water to achieve a pick‑up of 100 % ± 5 % of its own mass.
Test Procedure
Two tests are performed on each specimen: one dry and one wet. The rubbing cloth is mounted over the finger, and ten complete back‑and‑forth cycles are performed (five in each direction). After the test, the rubbed cloth is removed and conditioned again before evaluation. Staining on the rubbing cloth is rated by comparison with the Grey Scale for Staining (ISO 105‑A03) or using a spectrophotometer. The following table summarizes the key parameters:
| Parameter | Dry Test | Wet Test |
|---|---|---|
| Number of rubs | 10 | 10 |
| Stroke length | 104 mm | 104 mm |
| Finger force | 9 N ± 0.2 N | 9 N ± 0.2 N |
| Rubbing cloth moisture | Bone dry | 100 % ± 5 % wet pick‑up |
| Conditioning after test | As per standard | As per standard |
| Evaluation method | Grey Scale or instrument | Grey Scale or instrument |
Important: The wet rub test often yields lower ratings than the dry rub test. A rating of 3–4 is generally considered the minimum acceptable for apparel, but specific limits vary by end‑use and customer requirements.
Implementation Highlights
Successful implementation of CAN CGSB 4.2 No. 27.6-2015 in a laboratory requires attention to several practical details. First, the direction of rubbing should be consistent: for woven fabrics, rubbing is performed along the warp direction, unless otherwise agreed. For knitted fabrics, rubbing along the course direction is typical. The specimen must be held flat and taut during the test to avoid puckering, which can affect the contact geometry.
Another critical aspect is the preparation of the rubbing cloth. It must be free of any optical brighteners or chemical finishes that could artificially reduce staining. The cloth should be changed after each test to prevent carry‑over of colour from previous specimens. When multiple specimens are tested from the same lot, the average rating is reported. If the range exceeds one rating unit, additional tests are required.
Best Practice: Use a fresh, conditioned rubbing cloth for each test and avoid touching the test area with bare hands to prevent oil or moisture contamination that could skew results.
Compliance Notes
Compliance with CAN CGSB 4.2 No. 27.6-2015 is typically specified in purchasing contracts or product specifications. The standard does not define pass/fail criteria; these are established by the buyer and seller. However, a rating of 3 or lower is often considered poor and may lead to rejection. It is essential to distinguish between the two test conditions: a product may pass the dry test but fail the wet test, which is common for reactive‑dyed cottons.
The test report must include: the standard reference, the type of crockmeter used, the number of specimens, the individual and average ratings for both dry and wet tests, and any deviations from the standard procedure. Interlaboratory comparisons have shown good reproducibility when the equipment is properly maintained and the rubbing cloth is sourced from an approved supplier. Laboratories seeking accreditation under ISO/IEC 17025 should include this method in their scope and participate in proficiency testing programs.
Warning: If the staining on the rubbing cloth is uneven (e.g., heavier at one end), the test may be invalid. This often indicates improper mounting, excessive finger pressure variation, or a worn crockmeter finger. Inspect the apparatus and repeat the test.
Frequently Asked Questions
Q: What is the difference between CAN CGSB 4.2 No. 27.6-2015 and ISO 105‑X12?
A: Both standards describe essentially the same test procedure and use the same apparatus and rating system. CAN CGSB 4.2 No. 27.6-2015 is adopted by the Canadian General Standards Board and is technically equivalent to ISO 105‑X12. However, minor differences exist in the specification of the rubbing cloth (e.g., weight range and reflectance) and the conditioning requirements. Laboratories should verify which standard is referenced in their contract.
A: Both standards describe essentially the same test procedure and use the same apparatus and rating system. CAN CGSB 4.2 No. 27.6-2015 is adopted by the Canadian General Standards Board and is technically equivalent to ISO 105‑X12. However, minor differences exist in the specification of the rubbing cloth (e.g., weight range and reflectance) and the conditioning requirements. Laboratories should verify which standard is referenced in their contract.
Q: Why is the wet rub test more severe than the dry rub test?
A: Moisture can act as a swelling agent for fibres (especially cellulosic fibres), increasing the mobility of dye molecules and the mechanical abrasion effect. Additionally, water can carry surface dye deeper into the rubbing cloth, resulting in greater visible staining. Wet crocking fastness is often the most challenging performance criterion for deep shades of dye.
A: Moisture can act as a swelling agent for fibres (especially cellulosic fibres), increasing the mobility of dye molecules and the mechanical abrasion effect. Additionally, water can carry surface dye deeper into the rubbing cloth, resulting in greater visible staining. Wet crocking fastness is often the most challenging performance criterion for deep shades of dye.
Q: How can poor crocking fastness be improved?
A: Measures include using higher quality dyes, optimizing the dyeing process (e.g., better washing‑off after dyeing), applying a fixing agent, or adding a topical anti‑crock finish. For indigo denim, enzymatic washing and multiple rinse cycles are common. The choice of finishing chemicals can also significantly affect results.
A: Measures include using higher quality dyes, optimizing the dyeing process (e.g., better washing‑off after dyeing), applying a fixing agent, or adding a topical anti‑crock finish. For indigo denim, enzymatic washing and multiple rinse cycles are common. The choice of finishing chemicals can also significantly affect results.
Q: Is a spectrophotometer mandatory for evaluation?
A: No, visual comparison with the Grey Scale for Staining is the primary method and is acceptable for most purposes. Spectrophotometric evaluation is allowed and can provide more objective, continuous data. In case of dispute, visual assessment by a trained panellist is the referee method.
A: No, visual comparison with the Grey Scale for Staining is the primary method and is acceptable for most purposes. Spectrophotometric evaluation is allowed and can provide more objective, continuous data. In case of dispute, visual assessment by a trained panellist is the referee method.
This article is for informational purposes only. For official testing requirements, refer to the full text of CAN CGSB 4.2 No. 27.6-2015 published by the Canadian General Standards Board. Last updated 2026.