Leather Rubbing Colorfastness Testing

Leather colour fastness to rubbing testing mainly conducts scientific testing and analysis on dry rubbing colour fastness, wet rubbing colour fastness, perspiration rubbing colour fastness, organic solvent rubbing colour fastness, low-temperature rubbing colour fastness, and reciprocating rubbing and rotary rubbing, objectively assessing the product quality grade and issuing a detailed test report, providing a basis for manufacturers' quality control and downstream users' product acceptance.

Testing Items

Dry rubbing colour fastness: Refers to fixing a standard white rubbing cloth on the rubbing finger of the tester in the dry state, and after carrying out reciprocating rubbing on the leather surface, evaluating the degree of staining of the white rubbing cloth. This item is the most basic test item of leather colour fastness, directly reflecting the colour stability of leather under conventional dry contact conditions.

Wet rubbing colour fastness: Refers to wetting a standard white rubbing cloth with distilled water and wringing it dry to a specified moisture content, then carrying out reciprocating rubbing on the leather surface and evaluating its staining grade. This test simulates the colour transfer of leather under damp conditions (such as rainy days and perspiration contact), and is usually more stringent than the dry rubbing test.

Perspiration rubbing colour fastness: Refers to carrying out the test using a rubbing cloth wetted with a standard solution simulating acidic or alkaline perspiration. This item is specially for leather products that are in direct and long-term contact with human skin (such as shoe linings, clothing and gloves), evaluating the colour migration risk under the action of perspiration.

Organic solvent rubbing colour fastness: Refers to carrying out the test using a rubbing cloth wetted with a specific organic solvent (such as dimethylformamide). It is mainly used to evaluate some special leather products that may contact organic solvents, or to identify the colour fastness performance of certain types of dyes and finishing agents.

Low-temperature rubbing colour fastness: Refers to the rubbing colour fastness test carried out under a specific low-temperature environment (such as -10 ℃). For leather products used in cold climates, it evaluates whether the coating or dye is more likely to come off and transfer under low-temperature embrittlement conditions.

Reciprocating rubbing and rotary rubbing: Reciprocating rubbing simulates linear rubbing and is the mainstream method; rotary rubbing simulates a more complex rubbing track. The principles of the two methods are different, and the test results may differ, so the appropriate method needs to be selected according to the final use of the product and the relevant standards.

Testing Scope

Footwear leather: Covering all leather parts such as the upper, lining and insole. For the upper, dry/wet rubbing colour fastness needs to be focused on; for the lining and insole, the perspiration rubbing colour fastness test must be added, to prevent the socks or skin from being stained.

Leather for clothing and accessories: Including leather jackets, leather trousers, leather skirts, belts and leather bags. Such products are in close and frequent contact with the human body or other clothing, and have high requirements for dry, wet and perspiration rubbing colour fastness, especially since light-coloured clothing is easily stained by dark-coloured leather.

Leather for furniture and automotive interiors: Such as sofas, seats, steering wheel covers and automotive seat covers. Dry and wet rubbing colour fastness need to be tested, simulating daily use, cleaning and contact with human perspiration. Since automotive interior leather is often exposed to sunlight and high temperatures, rubbing tests sometimes need to be carried out after combining with light and heat aging.

Leather with special finishes: Such as polished color-change leather, pearlescent leather, metallic effect leather and suede. The special finish layer may affect the colour fastness, and during the test, special attention needs to be paid to the colour shedding form on the rubbing cloth (such as powdery shedding or overall transfer of the coating).

Dyed leather and coated leather: The colour of dyed leather penetrates into the interior of the leather fibres, while the colour of coated leather mainly exists in the surface finish layer. Generally, the rubbing colour fastness of high-quality dyed leather is better than that of leather coloured solely by the coating.

Leather at different production stages: The testing scope can cover the whole process from crust leather, dyed leather, finished leather after finishing to the final finished leather, to monitor the influence of the production process (such as dye fixation, fatliquoring and finishing) on the colour fastness.

Testing Methods

Standard reference method (GB/T 3920 / ISO 105-X12): The Chinese national standard GB/T 3920 "Textiles — Tests for colour fastness — Colour fastness to rubbing" is equivalent to ISO 105-X12, and is the most widely used basic method in the leather industry. It specifies the core parameters such as the diameter of the rubbing finger, pressure, stroke and number of reciprocations.

Leather-specific method (QB/T 2537 / IUF 450): QB/T 2537 "Leather — Tests for colour fastness — Colour fastness to rubbing with a reciprocating motion" is an industry standard more targeted at the characteristics of leather. IUF 450 is the standard method of the International Union of Leather Technologists and Chemists Societies (IULTCS) and has been adopted by many countries.

Test environmental conditions: Before the test, the sample and the rubbing cloth need to be conditioned under standard atmospheric conditions (such as a temperature of 20±2 ℃ and a relative humidity of 65±4%) for at least 4 hours. The environmental temperature and humidity affect the moisture content and softness of the leather, which in turn may affect the test results.

Specimen preparation: A specimen of not less than 50 mm × 200 mm is cut from a representative part and fixed on the base of the testing machine. For leather with patterns or uneven thickness, it is necessary to ensure that the test area is flat, and a hard board can be padded under the specimen if necessary.

Rubbing operation process: A standard cotton rubbing cloth (dry or wetted as specified) is smoothly wrapped on the cylindrical rubbing finger, the load is set to 9 N, and the rubbing finger carries out reciprocating rubbing 10 times along a straight track on the specimen at a rate of once per second. After the wet rubbing test, the rubbing cloth needs to be dried at room temperature.

Result rating method: The grey scale for assessing staining (GB/T 251 / ISO 105-A03) is used. Under a standard light source or north-facing natural light, the rubbed white cloth is compared with the original cloth to rate the staining grade. There are 5 grades in total, with grade 5 being the best (no staining) and grade 1 being the worst.

Testing Standards

Domestic Standards:

1. GB/T 3920-2024, Textiles — Tests for colour fastness — Colour fastness to rubbing

2. QB/T 2537, Leather — Tests for colour fastness — Colour fastness to rubbing with a reciprocating motion

3. GB 18401-2010, National general safety technical code for textile products

4. GB/T 3921-2008, Textiles — Tests for colour fastness — Colour fastness to washing with soap or soap and soda

International Standards:

1. ISO 105, Textiles — Tests for colour fastness

2. ISO 13934-1, Textiles — Tensile properties of fabrics — Part 1: Determination of maximum force and elongation at maximum force using the strip method

Note: The applicable standard can be selected according to the product use and customer trade requirements; standards agreed in the contract take precedence over general standards.

Testing Instruments and Equipment

Reciprocating rubbing colour fastness testing machine: The core equipment, in which a motor drives the rubbing finger to do horizontal reciprocating motion. The key components include a loading arm that can apply a specified pressure (usually 9 N or 10 N), a platform for fixing the specimen, a stroke counter and a speed controller. The equipment needs to run smoothly and the rubbing track should not deviate.

Standard rubbing finger: Usually a cylinder with a diameter of 16±0.1 mm, with a flat bottom, used for wrapping the rubbing cloth. The material, size and surface finish of the rubbing finger must comply with the standard requirements, to ensure that the contact area and pressure of each test are consistent.

Standard rubbing cloth: Bleached cotton cloth that is undyed and free of finishing agents, prepared according to the specified warp and weft density and mass per unit area. Before use, the selvedge needs to be removed and it needs to be checked that it does not contain fluorescent brightening agents. The quality of the rubbing cloth is one of the key factors affecting the reproducibility of the results.

Standard light source cabinet for rating: Provides D65 standard light source or other agreed light sources for observing and rating the staining grade. The interior of the cabinet is medium grey, which can shield the interference of external light, ensure the consistency and objectivity of the colour rating conditions, and reduce human visual errors.

Grey scale for assessing staining: Composed of a series of neutral grey chips representing the colour difference between the original sample and the stained sample, with each chip corresponding to a fastness grade (5, 4-5, 4, 3-4, 3, 2-3, 2, 1-2, 1). When rating, the grey scale and the specimen need to be placed on the same plane and observed at an angle of about 45°.

Auxiliary equipment: Including cutting knives for precisely cutting the specimen, squeezing devices or balances and measuring cylinders for adjusting the moisture content of the wet rubbing cloth, constant temperature and humidity chambers for conditioning the sample, and clamping devices for fixing the specimen to prevent movement.