Fig. 1

Design of a purpose-built chamber for IR analysis at controlled conditions of RH and gaseous atmosphere. a Schematic representation and b RGB image of the chamber. Thermal images were recorded with an IR-camera (FLIR A320) through an IR-transparent ZnS window, which was inclined at an angle of 15° to avoid reflexions. The environmental conditions of the atmosphere inside the chamber were monitored with a temperature and RH probe connected to a data logger, and O₂ concentration was also measured (see "Methods" for specific conditions in each Experiment). Two thermocouples were used to monitor the surface temperature of the rack, and of the liquid water below. An ultrasonic water vaporizer was used to rapidly generate a RH > 98% upon rehydration in the chamber. The water table could be elevated until the filter papers were imbibed from below, directly providing the samples with liquid water. For experiments under anoxia, N₂ gas was flushed through the chamber to replace the air, after humidifying the N₂ by bubbling it through a bottle with deionised water. The dimensions of the chamber were 36 cm length, 30 cm width, 44 cm depth, and 36 × 30 × 30 cm for the bottom part containing the samples. See "Methods" and Additional file 1 for further details