ISO 18915:2000

Overview

ISO 18915:2000 - "Imaging materials - Methods for the evaluation of the effectiveness of chemical conversion of silver images against oxidation" - specifies laboratory test methods for assessing how well chemical conversion treatments protect wet-processed silver-gelatin images from oxidative attack. It applies to silver-gelatin images on plastic, paper or glass supports. ISO 18915 describes two complementary test procedures (the dichromate bleach test and the hydrogen peroxide incubation test) and explains their significance; it does not prescribe specific stabilizing treatments, temperatures, times or replenishment rates.

Key topics and requirements

• Scope and applicability: Evaluates effectiveness of post-processing or in-process chemical conversion treatments intended to improve resistance to oxidizing pollutants (e.g., peroxides, ozone, NO2).
• Two test methods:
  • Dichromate bleach test - measures retained optical density after brief immersion in a potassium dichromate / sulfuric acid bleach to estimate fraction of silver converted to non‑bleachable forms. Results are expressed as percent density retention; ≈65% density retention or higher across six density patches is indicated in the standard as representative of a stable image.
  • Hydrogen peroxide incubation test - exposes specimens to hydrogen peroxide vapour under controlled humidity and temperature and measures density change to assess peroxide resistance. The method specifies apparatus (desiccator with fan and baffles, salt-saturated humidity control), peroxide dosing and an oven temperature for incubation.
• Specimen preparation and measurement: Both methods use six uniform-density patches spanning a density range; densitometric measurements are made in conformance with ISO 5-series (ISO 5-2, 5-3, 5-4) and status A blue density conventions.
• Normative and informative annexes: Annex D provides density-correction procedures; Annex B discusses variables in stabilizing treatments; Annex C addresses test significance.

Practical applications and users

• Preservation labs and archives evaluating chemical stabilization options for historical black-and-white photographic collections.
• Photographic materials manufacturers validating anti-oxidation processing steps (e.g., sulfiding, seleniding, gold substitution).
• Conservation scientists and imaging researchers comparing treatment performance and establishing acceptance criteria for image permanence.
• Quality control teams assessing batch-to-batch consistency of stabilization treatments.

Related standards

• ISO 5-2, ISO 5-3, ISO 5-4 - densitometry and measurement conditions.
• ISO 18901, 18902, 18911, 18918, 18920 - companion standards on processed silver-gelatin material properties, storage and handling, and archival practices.

ISO 18915 is a targeted, test-method standard for quantifying the oxidative stability conferred by chemical conversion treatments, helping professionals make evidence-based decisions about photographic image stability and long-term preservation.