This is a sampling of prepared photopaper strips that were placed in various positions above a series of vents within the sulfidic portions of the Frasassi Caves in Italy. These vents led to an underground stream releasing H2S which was about 8 meters below. At the lip of the vents H2S concentrations were approximately 4-8 ppm and this quickly dropped into sub ppm levels within several meters. Despite low levels, the odor of H2S was very strong.
The photo paper strips were prepared as described by Horwell (2004) and were exposed to a sulfidic atmosphere for a period of approximately one to two days. The prepared paper was stored within black film canisters in a U-shape so the middle of the strip was at the base of the container and the edges were near the opening. The caves were very humid and lighter spots formed as a result of water accumulation on the paper. In most cases, canisters were positioned on their sides so drip water could not fall in. For storage and scanning purposes, the strips were pasted onto 3x5 index cards after being fixed. These images have been reduced in resolution for easier sharing.
Test strip #3 was a test to see if the color would change within a reasonable time frame for field work. H2¬S concentrations were likely on the order of 2-3 ppm in this area and the paper was exposed for approximately 48 hours.
Test strip #26 was positioned several meters away from the H2S vents for slightly less than 1 day and likely experienced concentrations less than or near 1 ppm.
Test strip #20 was exposed to the atmosphere near one of the vents and likely experienced H2S concentrations of 3-4 ppm.