Overview - ISO 18914:2013 (wet abrasion test for imaging materials)
ISO 18914:2013 defines a laboratory method for determining the resistance of photographic emulsions and gelatin backings to wet abrasion during processing. Commonly called the “mushiness” or wet scratch-resistance test, it measures the force (in grams) at which a stylus digs into a wet emulsion. The standard applies to photographic film and paper emulsions when wet and is intended for controlled comparisons of processing variables, emulsion formulations, ageing effects, and post‑processing treatments.
Keywords: ISO 18914, wet abrasion, photographic emulsions, gelatin layers, scratch resistance, imaging materials
Key topics and technical requirements
- Test scope: Applies only to wet emulsion or gelatin layers (not the support material).
- Specimens: Representative samples, typically 35 mm × ~250 mm; can be unprocessed or processed (clear/D).
- Apparatus:
- Immersion tray that moves smoothly at least 30 mm horizontally (manual or power driven).
- Spherical stylus (sapphire or diamond) mounted on a pivoted arm; 0.38 mm radius for film-base emulsions and 0.20 mm radius for paper-base emulsions.
- Two instrument formats: constant-load (weights from ~1 g to 210 g) and continuous-load (weight increases from 0 g to 70 g over travel; additional weights up to 150 g possible).
- Procedure:
- Specimen immersed in distilled water or actual processing solution at test temperature.
- Tray is drawn under the stylus completing travel in 1–2 s; three scratch lines (≥30 mm) per load.
- For multi-step processing, specimens are pre-immersed sequentially in prior solutions to simulate real processing.
- Rating and interpretation:
- The wet-abrasion (mushiness) value = grams on the stylus that cause penetration.
- Ratings may be made by reflected or transmitted light, wet or after drying.
- Note: results from constant-load and continuous-load instruments may not be directly comparable. Typical significance thresholds are provided (e.g., 5 g below 20 g, 10 g between 40–100 g).
Applications and who uses this standard
- Quality assurance and R&D for photographic film and paper manufacturers to:
- Compare emulsion formulations and gelatin treatments.
- Evaluate effects of processing solutions, temperatures, times, and ageing on wet scratch resistance.
- Conservation scientists and photographic labs assessing physical integrity of historical or experimental materials.
- Equipment designers and process engineers optimizing processing lines to reduce abrasion damage.
Related standards
- ISO 18922 - Processed photographic films - Methods for determining dry scratch resistance (referenced for dry testing and related methodology).
This standard is essential when assessing wet mechanical durability of imaging materials and for rigorous, repeatable evaluation of processing and formulation impacts on emulsion integrity.