Indigo transfer, or crocking, is a perennial concern for denim fabrics. When a denim garment rubs against skin, other garments, or accessories, pigment can migrate from the warp and weft to nearby surfaces. For OEM/ODM producers like Newasia Garment, a robust rubbing test is not just a laboratory convenience—it is a risk-management tool that protects your clients’ brands, reduces post-production returns, and guarantees consistent color performance across batches. This article dives into a practical, multi-style guide to the rubbing test for indigo transfer, blending technical detail with hands-on guidance and real-world factory workflow insights.
Indigo and Crocking: Why Rubbing Fastness Matters in Denim
Indigo is a classic vat dye that behaves differently from reactive or disperse dyes. In denim, indigo molecules often reside on the surface of the fibers rather than fully penetrating the yarns. The result can be excellent initial color depth but variable colorfastness under abrasion or friction. Consumers expect jeans to retain color on the fabric itself while minimizing excess transfer to the wearer’s skin, underwear, or light-colored fabrics such as white shirts. A rubbing test quantifies how much indigo pigment migrates during simulated wear—providing a standardized metric to compare grades of dyeing, finishing, and fabric construction. For Newasia’s OEM/ODM workflows, incorporating a rigorously defined crocking test helps ensure that every denim style—from classic indigo to specialty finishes—meets cross-border quality expectations.
Standards and Methods: What Guides the Test
There are several established methods used globally to assess rubbing fastness. The two most relevant for indigo transfer on denim are colorfastness to crocking and colorfastness to rubbing, often referred to by standard numbers such as AATCC 8 and ISO 105-X12. In practice, manufacturers perform both dry and wet Crocking tests to capture different friction scenarios. Here is a quick map of what you’ll encounter in a modern test lab:
- AATCC 8: Colorfastness to Crocking. This is the classic method where a white test fabric or a mineral gray scale is rubbed against a dyed fabric or vice versa. Results are reported for both dry and wet rubbing, with ratings typically on a scale that reflects staining on the receiver fabric and color change on the tested fabric.
- ISO 105-X12: Colour fastness to rubbing (crocking). A similar approach with internationally harmonized test cycles, apparatus, and rating scales. ISO 105-X12 emphasizes reproducibility across different climates and laboratories, which matters for global supply chains like those served by Newasia Garment.
- Gray scale for staining and color change. The gray scales provide a qualitative rating: from no staining or change (highly colorfast) to heavy staining or color change (low colorfastness). While the numeric system differs by standard, the principle remains: quantify both dye loss from the sample and dye deposition on the rubbing cloth.
In practice, many denim manufacturers report results for both dry and wet rubbing, and for both directions of contact (fabric to test cloth and test cloth to fabric) to capture the full risk profile of a given denim lot. This dual approach is essential when indigo transfer is a concern, because wet conditions greatly amplify the mobility of indigo on the fabric surface.
Equipment, Setup, and Materials: What You Need in a Modern Lab
To perform a reliable rubbing test, you need a compact, repeatable setup. A modern lab at an OEM/ODM facility like Newasia typically includes:
- Crockmeter or equivalent rubbing device. This device slides or rotates a weighted rubbing head across a test cloth in a controlled manner and cycle count.
- White test cloths. Usually bleached cotton or a standard cotton fabric around 6–12 cm wide, cut into squares for the receiver surface or to accompany the tested fabric depending on the method.
- Specimens of dyed denim. Cut to uniform dimensions with edges sealed to avoid unraveling, typically 50 × 100 mm or similar depending on the spec.
- Standard weights and cycle counts. Common methods use weights in the 0.5–1.0 kg range with 10–20 cycles for denim trials, though some protocols call for more cycles to simulate longer wear.
- Conditioning cabinet. A controlled environment (temperature and humidity) to stabilize samples before testing, typically around 20–23°C and 50–65% RH.
- Gray scale and documentation templates. For consistent interpretation of results, testers refer to the Gray Scale for Staining and the Gray Scale for Color Change, and record results in a standardized data sheet.
At Newasia, we align lab practices with international guidelines and tailor the test matrix to each denim style. That means choosing the correct cycles, whether to test wet vs dry rubbing, and deciding if a double-direction rub (one pass in each direction) reveals more about a fabric’s propensity to crock in real wear.
Performing the Test: Step-by-Step Instructions
The following procedure reflects a practical, production-friendly rub-test workflow suitable for a denim-focused OEM/ODM environment. It emphasizes repeatability and clarity for colorfastness reporting.
- Prepare the specimens: Cut dyed denim swatches and corresponding white test cloths. Label each pair with lot numbers, dye recipe references, and finishing steps if applicable. Ensure edges are finished to prevent fraying, and allow samples to dry completely before testing.
- Condition the samples: Place all specimens and test cloths in a conditioning chamber set to standard atmospheric conditions (20–23°C; 50–65% RH) for 24 hours. Conditioning minimizes variability due to moisture content and ambient humidity.
- Decide wet vs dry rubbing: A wet rubbing test uses a dampened test cloth or a speciment-specific conditioning state, while a dry rubbing test uses a dry test cloth. Wet rubbing more closely simulates wear that involves moisture or perspiration, which often intensifies indigo transfer on denim.
- Set up the Crockmeter: Secure the dyed denim specimen in the instrument’s clamp with consistent tension. Attach the white test cloth to the rubbing pad or counter surface according to the device’s manual. Choose the weight and cycle count based on your standard (commonly 10–20 cycles for denim, with 1–2 direction passes per cycle).
- Run the test: Initiate the rubbing sequence under controlled conditions. After completion, remove the cloth and the tested fabric carefully without disturbing staining patterns. Record the exact cycle count, weight, and any deviations from the standard.
- Evaluate color transfer: Examine the white test cloth for staining. Use the gray scale for staining to assign a numerical score ranging from 5 (no staining) to 1 (heavy staining). Then, examine the dyed fabric for color change using the gray scale for color change if necessary. Document both results in the test log.
- Document the results: Take high-quality images of the stained receiver cloth and note the color change of the sample. Record the reporting metrics as dry crocking rating and wet crocking rating, including any observations about surface abrasion or fiber raise that might influence results.
- Review and act: Compare results against internal pass/fail criteria or client specifications. If crocking is higher than acceptable, identify potential adjustments in dyeing, finishing, or fabric construction to improve fastness before mass production.
Interpreting the Data: From Numbers to Decisions
A typical reporting format for indigo crocking includes:
- Dry crocking rating for the sample on the textile side.
- Wet crocking rating for the sample on the textile side.
- Staining rating on the receiver fabric (white cloth) for both dry and wet conditions.
- Color change rating for the dyed denim, if applicable, to capture subtle hue shifts that accompany pigment loss or migration.
- Notes about finishing conditions (stone washing, enzyme wash, pad-dry, resin finishing) that can influence crocking behavior.
In general, a higher dry crocking rating (closer to 5) and a higher staining rating on the receiver cloth (closer to 5) indicate poorer colorfastness to rubbing. Wet rubbing results often are more stringent, because moisture facilitates indigo migration. Producers should aim for high ratings in both dry and wet tests, and especially for receiver cloth staining, which directly correlates with consumer-visible color transfer.
Strategies to Improve Indigo Colorfastness on Denim
When indigo transfer is a concern, a multi-pronged approach yields the best long-term results. Here are practical strategies used by leading denim manufacturers and OEMs to reduce crocking while maintaining the aesthetic and hand feel expected from premium jeans:
- Optimize dyeing process: Ensure complete exhaustion of indigo during the dyeing cycle. Incomplete fixation leaves more dye on the surface, increasing transfer risk. Adjust dye bath chemistry, temperature, and reducing agents to promote deeper fixation.
- Enhance post-dye finishing: Finishing steps such as washing, scouring, and diffusion patterns can influence crocking. Controlled enzyme washes and stone-wash steps can help. Avoid overly aggressive finishing that abrades the surface, which can release indigo.
- Apply surface finishes judiciously: Certain resin-based finishes or anti-fade treatments can help lock dye in place after dyeing. Test these finishes for their impact on handle, appearance, and wash durability to avoid trade-offs that customers notice.
- Control fabric structure and weight: Denser yarns and tighter weaves can reduce pigment migration. However, this must be balanced with comfort and fit considerations for the end product.
- Quality through process integration: Implement inline colorfastness checks during production runs. Real-time crocking tests on representative fabric panels help catch issues before large-scale production.
- Standardize testing across lots: Use a consistent testing matrix (cycles, weights, conditioning) across all lots for comparability. Document any deviations and their impact on crocking results.
Case Study: Newasia’s Approach to Indigo Fastness in Denim Lines
Newasia Garment, a long-standing OEM/ODM partner, maintains a dedicated textiles lab that mirrors this approach. With extensive experience in denim, we run colorfastness to crocking tests on every new denim recipe—warp/weft, weight range, and finishing variants included. Our process begins with a thorough review of the dye chemistry and the intended end-use: casual denim, workwear, or abrasion-heavy fashion lines. We then craft a test matrix that covers both dry and wet rubbing, multiple cycle counts, and standardized receiver fabrics. The lab collects data, compares against client specifications, and provides actionable recommendations to the production team. This disciplined testing discipline supports rapid development cycles, reduces risk, and helps ensure consistent color performance across global markets.
Practical Tips for Running an Efficient Rubbing Test in a Denim Enterprise
To keep the process efficient while delivering reliable results, try these tactics in your plant or contract facility:
- Standardize specimen sizes and cutting patterns to minimize sample-to-sample variability.
- Condition all specimens uniformly before testing; small humidity differences can skew results, particularly for wet rubs.
- Use a single, well-calibrated Crockmeter for all tests in a given lot to ensure comparability across runs.
- Train technicians to apply consistent weight and cycle cycles and to assess graying or staining on a fixed scale.
- Maintain an audit trail: keep raw data, photos, and notes for every test to support traceability and client reviews.
Q&A: Quick Answers for Industry Practitioners
Q: How many rubbing cycles should I use for a denim crocking test?
A: It depends on your target market and client specs. Common ranges are 10–20 cycles for preliminary screening, or more cycles (20–40) for deeper reliability and to simulate longer wear. Wet rubbing tests generally require the higher end of cycles to reflect moisture-enhanced transfer.
Q: Is crocking testing necessary for all denim products?
A: For products with strict colorfastness requirements or high consumer expectations (premium jeans, fashion collaborations, and brands emphasizing wash effects), crocking testing is essential. It is also valuable for new dye batches or finishing technologies where color stability is uncertain.
Q: How can I reduce indigo crocking without sacrificing hand feel?
A: Focus on dye exhaustion, optimize post-dye finishing, and consider compatible surface finishes. Always validate any finish with a small pilot run to ensure it doesn’t compromise the fabric’s comfort or look.
Q: What role does standardization play in cross-border supply chains?
A: Very significant. International standards (AATCC, ISO) ensure your tests are meaningful across laboratories and markets, enabling smoother audits and consistent product performance for global brands.
Putting It All Together: The Value of a Robust Rubbing Test in Denim Programs
For a denim OEM/ODM partner like Newasia, the rubbing test for indigo transfer is more than a quality check—it is a strategic tool that aligns product performance with consumer expectations. A rigorous crocking test helps you identify weak finishes, optimize dyeing strategies, and present data-driven assurances to clients. It also supports sustainability goals by reducing returns and remanufacturing related to color transfer, ultimately strengthening brand trust in markets where colorfastness is a top buying criterion.
In the daily workflow of fabric development and mass production, the rubbing test is a touchstone that connects chemistry, engineering, and consumer experience. It informs decisions about dye chemistry, finishing chemistry, fabric construction, and quality control protocols. When executed with discipline, it yields actionable insights that protect both brand reputation and the bottom line.
