To increase the severity of the test conditions, the sample and metal foil may be allowed to make slight contact. In addition, a small test tube containing 1 ml of distilled water is placed in each container to maintain a constant relative humidity of approximately 100%. The containers are then kept in a drying oven for 28 days at 60 °C.

Metal specifications:

• Lead: thickness 0.1 mm, purity 99.95%, pieces 50 × 50 mm, hardness: as rolled
• Silver: thickness 0.25 mm, purity 99.95+%, pieces 50 × 50 mm, hardness: as rolled
• Copper: thickness 0.125 mm, purity 99.9%, pieces 50 × 50 mm, hardness: hard

If corrosion appears on the metal coupons after the 28-day exposure, it indicates the emission of the following compounds:

• Silver: sulfur compounds
• Copper: chlorides, oxides, sulfur compounds
• Lead: organic acids and aldehydes

Evaluation of results:

• P = Permanent: No visible corrosion; a red-orange iridescence often appears on the copper reference. The coupon should retain its polish, and the lead may show a purplish sheen. Material suitable for permanent use.
• T = Temporary: Slight discoloration or corrosion films, often along the lower edges or sides; few localized corrosion spots. Suitable for temporary storage (< 6 months).
• U = Unsuitable: Clearly visible corrosion. Material unsuitable for use in exhibitions or storage.