AATCC TM8: Understanding colorfastness to crocking in fabrics

Often simply referred to as ‘crocking,’ AATCC Test Method 8 (AATCC TM8) is a widely recognized and essential procedure for evaluating colorfastness to crocking. It describes a fabric's ability to resist the transfer of color from its surface to another material or object through rubbing.  

The standardized approach

Developed by the American Association of Textile Chemists and Colorists (AATCC), the ‘Test Method for Colorfastness to Crocking: Crockmeter Method,’ AATCC TM8 is applicable to textiles made from all fiber types, whether dyed, printed, or otherwise colored, and can be used for yarn or fabric forms.

The core of the AATCC TM8 test revolves around a specialized instrument called a Crockmeter. This device ensures a consistent and controlled rubbing action, eliminating variability that would occur with manual rubbing.

Test procedure: Dry and wet crocking

The AATCC TM8 method typically involves two main tests:

Dry crocking: A colored test specimen of the fabric is securely mounted on the base of the Crockmeter. After this a square of standardized white cotton test cloth is attached to the rubbing finger of the Crockmeter. This white cloth acts as the receiving material for any transferred color. Under a specified downward force, the rubbing finger is moved back and forth across the surface of the colored specimen for a set number of cycles. After the rubbing is complete, the white test cloth is removed.

Wet crocking: This procedure is similar to dry crocking, but with a crucial difference: the white cotton test cloth is pre-moistened with distilled water to a specified moisture content before being attached to the rubbing finger.

The wet test simulates conditions where fabric might be exposed to moisture, such as perspiration, rain, or dampness, which can significantly increase the likelihood of dye transfer.After rubbing, the wet white test cloth is removed and allowed to dry.

Evaluation and grading

Once the dry and wet white test cloths have been subjected to the rubbing action and are dry, the extent of color transfer is evaluated. This is done by comparing the stained white test cloths to standardized scales:

• AATCC Gray Scale for Staining (AATCC Evaluation Procedure 2): This scale consists of five pairs of gray chips, representing different degrees of staining, from Grade 5 (no staining) to Grade 1 (heavy staining). Intermediate ratings (e.g., 4-5, 3-4) can also be assigned for finer differentiation.
• AATCC Chromatic Transference Scale (AATCC Evaluation Procedure 8): This scale provides a more nuanced visual assessment, with specific color chips to help evaluate the shade and intensity of transferred color.

Factors influencing crocking performance

Several factors can affect a fabric's colorfastness to crocking, and understanding these is crucial for manufacturers to improve product quality:

• Dye type and fixation: Poorly fixed dyes or those that have a tendency to aggregate on the fiber surface are more prone to crocking.
• Fabric construction: Fabrics with a rough surface, such as brushed, napped, or piled fabrics tend to exhibit more crocking due to the increased surface area and loose fibers that can rub off.
• Finishing treatments: Certain finishing agents, particularly softeners or those that create a surface coating can sometimes trap unfixed dye particles or create a less stable surface, thereby impacting crockfastness.
• Washing and after-treatment: Inadequate washing-off of unfixed dyes after the dyeing process is a major contributor to poor crockfastness.
• Fiber type: Different fibers interact with dyes in distinct ways. For example, cotton, a cellulosic fiber, can be more prone to wet crocking if not properly dyed and washed, due to its absorbency and potential for microfibril formation.

Importance in the textile industry

AATCC TM8 serves as a vital tool for

• Quality control: Manufacturers use this test method to monitor the quality of their dyeing and finishing processes, identifying and correcting issues that lead to poor crockfastness.
• Product development: It guides the selection of appropriate dyes, chemicals, and finishing treatments to meet desired performance standards.
• Supplier specifications: Brands and retailers rely on AATCC TM8 results to set colorfastness requirements for their textile suppliers, ensuring consistency across their product lines.

By adhering to the principles and procedures outlined in AATCC TM8, the textile industry can consistently produce fabrics that maintain their color integrity, even under the stresses of everyday rubbing and wear, thereby delivering greater value and satisfaction to the end-user.