Leather Inspection

Leather inspection mainly conducts scientific testing and analysis on physical and mechanical property inspection, chemical property inspection, colour fastness inspection, appearance and sensory inspection, material identification and special property inspection, 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

Physical and mechanical property inspection: This is the core for evaluating the durability and applicability of the leather. It mainly includes the tensile strength, elongation at break, tearing strength, bursting height (bursting strength) and flexing endurance, to judge the performance of the leather under use conditions such as stress, tension and bending.

Chemical property inspection: Aimed at analysing the chemical composition and stability of the leather. The key items include the pH value and dilution difference, hexavalent chromium content, formaldehyde content, prohibited azo dyes, pentachlorophenol content and volatile substance content, which are directly related to the ecological safety of leather products and human health.

Colour fastness inspection: Evaluates the fastness of the leather colour under the action of external factors. The conventional inspection items cover the colour fastness to rubbing (dry/wet), colour fastness to perspiration, colour fastness to light, colour fastness to water spotting and colour fastness to hot pressing, which directly affect the appearance retention and use safety of the product.

Appearance and sensory inspection: In accordance with the standards or the agreement of both parties, a judgement combining subjectivity and objectivity is made on the surface condition of the leather. It mainly includes the colour uniformity, lustre, pattern definition, coating adhesion firmness, grain defects (such as loose grain and piping) and thickness uniformity.

Material identification: Identifies the authenticity and type of the leather through chemical or physical methods. For example, distinguishing genuine leather from artificial leather, or identifying the animal type (such as cowhide, sheepskin and pigskin). Microscope observation of the fibre structure is a common identification method.

Special property inspection: Targeted tests are carried out according to the final use of the leather. For example, shoe leather needs to test the perspiration resistance and dynamic waterproofness; furniture leather needs to test the colour fastness to dry/wet rubbing and flame retardancy; and automotive leather needs to focus on the light resistance, heat aging resistance and fogging value.

Testing Scope

Classification by processing technology: Including chrome-tanned leather, vegetable-tanned leather, aldehyde-tanned leather, oil-tanned leather and combination-tanned leather. Different tanning processes give the leather quite different characteristics, and the inspection emphasis is different. For example, vegetable-tanned leather needs to focus on the tearing strength, while chrome-tanned leather needs to strictly control the hexavalent chromium content.

Classification by animal raw material: Covering mammal hides (such as cowhide, sheepskin and pigskin), reptile skins (such as crocodile skin and snake skin), fish skins (such as shark skin) and other special skins (such as ostrich skin). The fibre structures of different raw hides differ significantly, which is the main basis for the material identification.

Classification by surface state: Including full-grain leather, corrected-grain leather, suede leather (top suede and reverse suede), polished effect leather, embossed leather and patent leather. During inspection, targeted attention needs to be paid to their surface characteristics, such as the colour uniformity and pile firmness of suede leather, and the coating adhesion firmness and flexing resistance of patent leather.

Classification by final use: This is the most practical classification method. It mainly includes shoe upper leather, shoe lining leather, garment leather, furniture leather (sofa leather), automobile seat leather, packaging leather, ball leather and industrial leather. Different uses correspond to different standard systems and key performance indicators.

Classification by finished product form: The testing objects can be whole wet-blue leather, finished leather, or the made semi-finished products or final products (such as leather shoes, leather clothes and leather bags). When testing finished products, the sampling position and method need to strictly follow the relevant standards.

Ecological leather and special function leather: With the regulatory and market requirements, for leather that meets specific ecological standards (such as OEKO-TEX® STANDARD 100 and LWG) and leather with special functions such as waterproofness, flame retardancy and antibacterial properties, the testing scope will be extended to more hazardous substances and function verification items.

Testing Methods

Physical property test methods: Mainly in accordance with the ISO, ASTM and GB/T standards. For example, the tensile strength and elongation at break are usually determined in accordance with ISO 3376 or GB/T 4689.5, using a universal material testing machine; the tearing strength is determined in accordance with ISO 3377-2 (double-edge tear); the flexing endurance is tested with a bursting tester or flexing tester in accordance with ISO 5402 or GB/T 4689.9 by reciprocating bending.

Chemical analysis test methods: Mostly adopting the combination of instrumental analysis and chemical titration. The pH value and dilution difference are determined in accordance with ISO 4045; the hexavalent chromium content is detected by the spectrophotometric method in accordance with ISO 17075; the formaldehyde content is usually determined in accordance with ISO 17226-1 (high-performance liquid chromatography method) or ISO 17226-2 (colorimetric method); the prohibited azo dyes are detected in accordance with the ISO 17234 standard series, using gas chromatography-mass spectrometry (GC-MS).

Colour fastness test methods: Simulate the actual use conditions. The colour fastness to rubbing is in accordance with ISO 11640, using a rubbing fastness tester for dry/wet rubbing; the colour fastness to perspiration is in accordance with ISO 11641, soaking the specimen with a standard adjacent fabric in artificial perspiration and then pressing; the colour fastness to light is in accordance with ISO 105-B02, using a xenon arc lamp aging chamber to simulate light exposure.

Material identification methods: The most reliable method is the micro-section method. In accordance with the IULTCS/IUF methods, the leather sample is made into a cross-section slice, and the fibre structure characteristics are observed under an optical microscope and compared with the standard atlases, thereby accurately identifying the authenticity and the animal type.

Appearance and sensory inspection methods: Usually carried out under a standard light source cabinet (such as the D65 light source). Experienced inspectors make judgements on the colour, lustre and defects at the specified observation distance and angle, comparing with the standard samples or the reference samples confirmed by both parties. It has a certain subjectivity but needs to follow the standard procedures.

Special property test methods: The methods are highly targeted. For example, the fogging value test of automotive leather is in accordance with ISO 17071 (gloss method) or ISO 17072 (gravimetric method); the flame retardancy test may be in accordance with FMVSS 302 or GB 8410; the dynamic waterproofness test simulates the water penetration when walking, carried out in accordance with methods such as SATRA TM92.

Testing Standards

Domestic Standards:

1. GB/T 4689.9, Leather — Physical and mechanical tests — Determination of flex resistance

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

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

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

International Standards:

1. ISO 3376, Leather — Physical and mechanical tests — Determination of tensile strength and percentage extension

2. ISO 17075, Leather — Chemical tests — Determination of chromium(VI) content

3. ISO 5402, Leather — Physical and mechanical tests — Determination of flex resistance

4. ISO 105, Textiles — Tests for colour fastness

5. 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

General physical property testing equipment: The universal material testing machine is the core equipment for testing the strengths such as tensile and tearing; the bursting height tester (bursting tester) is used to evaluate the top extension strength of the leather; the leather flexing tester is used to simulate the damage caused to the leather by repeated bending; and the thickness gauge is used to precisely measure the thickness of each part.

Chemical analysis instruments: The pH meter is used to measure the pH value of the leather extract; the UV-visible spectrophotometer is used to determine the contents of substances such as hexavalent chromium and formaldehyde (colorimetric method); the high-performance liquid chromatograph (HPLC) is used to precisely determine the formaldehyde monomer; and the gas chromatography-mass spectrometer (GC-MS) is the key equipment for detecting complex organic substances such as prohibited azo dyes and phenols.

Colour fastness testing equipment: The rubbing fastness tester is essential equipment for the dry and wet rubbing tests; the perspiration fastness tester provides constant temperature and pressure conditions; the xenon arc lamp aging test chamber is used to simulate sunlight exposure and evaluate the colour fastness to light; and there are also dedicated devices for the water spotting and hot pressing tests.

Material identification and micro observation equipment: The optical microscope (equipped with a camera system) is the main tool for the micro analysis of the leather fibre structure, and needs to be combined with a microtome and dyeing equipment for sample preparation. The scanning electron microscope (SEM) can be used for the observation of ultra-micro structures at higher magnifications.

Environmental simulation and aging equipment: The constant temperature and humidity chamber is used for the conditioning of the specimens and the environmental control of the wet-state tests; the low-temperature freezer is used to test the performance of the leather at low temperatures; and the heat aging chamber is used to evaluate the stability of the leather at high temperatures and the odour changes.

Auxiliary and dedicated equipment: The standard light source colour matching cabinet provides a stable and consistent light source for the appearance inspection; the fogging tester is specially used for the volatility testing of automotive interior materials; the air permeability tester and water vapour permeability tester are used to evaluate the hygienic performance of the leather; and the flame retardancy testing device is used to evaluate the combustion characteristics of the material.