Overview
ISO 18907:2013 - Imaging materials - Photographic films and papers - Wedge test for brittleness - defines a standardized laboratory method to measure and express the brittleness of photographic films and papers. The method applies to films with or without gelatin backing and to fibre‑based or resin‑coated (RC) photographic papers, and can be used on raw or processed materials. The standard is widely used in imaging materials quality control, product development, and conservation testing.
Key Topics and Requirements
- Principle: determine the wedge opening at which a specimen loop fails when subjected to a rapid folding (high strain) action.
- Apparatus:
- Wedge tester: two non‑parallel metal jaws forming a V. Two standardized designs:
- Narrow wedge: 9° angle, maximum opening 25 mm (typical for most films).
- Wide wedge: 28° angle, maximum opening 74 mm (recommended for more brittle materials).
- Test chamber: temperature and relative humidity tightly controlled (air velocity ≥ 15 cm/s).
- Specimen preparation and sampling:
- Standard specimen size: 350 mm long × 15–16 mm wide; set of 10 specimens per test.
- Cut specimens in 20–23 °C and 40–55 % RH; wear gloves and use precision cutter.
- Test samples in machine and transverse directions where possible; test backed films with backing convex.
- Conditioning and test conditions:
- Standard test conditions: (15 ± 1) % RH and 23 °C ± 1 °C (other RH or temperatures may be used for studies).
- Typical conditioning times: ~4 h for films, ~1 day for fibre papers, ~7 days for RC papers (varies by thickness and exposure).
- Procedure and reporting:
- Loop specimen emulsion side out; pull through narrow opening in a smooth motion (completed within 1 s); read wedge separation at failure to nearest 0.5 mm.
- Record both first emulsion crack and complete material break when applicable.
- Limitations: brittleness depends strongly on humidity, temperature, thickness and handling; wedge test is one indicator and not universally predictive for all stress types.
Applications
- Quality control for photographic film and paper manufacturing
- Comparative materials testing during product development
- Archival and conservation assessment of photographic materials
- Failure analysis for imaging equipment and handling procedures
Related Standards
- ISO 483 - used for accurate humidity control in conditioning and testing environments.
Keywords: ISO 18907:2013, wedge test for brittleness, photographic films, photographic papers, brittleness testing, conditioning, wedge tester, RC papers, fibre‑based papers.
