Public Lab Research note

H2S film strip test #2

by Shannon | January 30, 2012 04:11 30 Jan 04:11 | #725 | #725

Last Thursday, students in the joint Public Lab and RISD Environmental Justice Research Cluster met for the second round of making film strips to test for hydrogen sulfide. Read more about the work in progress here and what the idea behind using film is: We met at the AS220 darkroom and were able to do the mix for the paper coating, cutting strips and paper drying in this space. A couple of images are here.

A few issues came up that need to be resolved (and we'd love to hear from you if you have suggestions):

  • Darkroom access- we weren't able to work in the normal RISD building because we were using Photo Flo (which can be washed down the drain, but should have proper ventilation when used). We did get immediate access to the AS220 darkroom down the street however. Problematically we had to request that the white light in the film processing room remain off while we dried the strips for 12+ hours. When people use the paper for tests, they will also have to send back to someone that has access to a darkroom to process the strips. When trying to test for H2S presence immediately (such as using a bucket for a follow-up grab sample), this time gap could be an issue.

  • The glycerol on the paper was supposed to be "dry" after 12 hours. We took the strips down after 16 hours and they were a sticky/oily consistency. Need to figure out the meaning of the word "dry" in this context and if we are getting the correct result.

  • Packaging for shipping the strips is going to be tricky. We were initially thinking that making an envelope out of a black trash bag would work, but the black bags that photo paper comes in is much thicker than a normal trash bag. After talking with a couple photo shops in the Providence area, the agreement was not to use trash bags, might need to get an industrial black plastic roll. Second issue with these envelopes is that at least one side will need to be double layered so that both layers can have slits that will let some air flow in without exposing the paper to light.

  • Amber filter safe lights are hard to come by if you want to make your own darkroom! In the Boston/Providence area, after calling 10 shops, we finally found a store that had one in stock. I found a post about making sure safelights are actually safe: and will do some searching to see if there are easy ways to just make these lights- paying $15-$40 for a lightbulb isn't all that attractive to me.

  • To use salt or not to use salt- adding salt to the glycerol/water/photo flo combination is "optional". This batch we did not use salt, will need to try it with salt at some point.


We should test the darkroom safelights with a spectrometer!

Interesting presentation on darkroom safelights here (but dated to 1982, so out of date):

As Wikipedia states, "A safelight is a light source suitable for use in a photographic darkroom. It provides illumination only from parts of the visible spectrum to which the photographic material in use is nearly or completely insensitive."

Such a light might have a spectrum not dissimilar from this:

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I realized none of our notes so far cover how to make the glycerol solution, here is that protocol:

1) Wear plastic gloves and use thongs while making this mixture and handling the strips. Work in a room with good ventilation.

2) Make a 50/50 mix of water and glycerol in a tray Add 5 gram of Sodium Chloride (optional) Add 5 drops of surfactant Kodak Photoflo 200. (MSDS for Kodak Photo Flo 200)

3) In a dark room, use thongs to place the cut strips of photopaper into this mixture for five minutes

4) Remove the strips with thongs and place them on paper towels to dry for five minutes

5) Then leave them to dry in a dark room for twelve hours (we have been hanging them using clothes pins)

6) After 12 hours, in the dark room place the strips with tweezers into containers for testing.

7) Waste Disposal: If you are working in a school or professional darkroom, follow their procedures for safe disposal of the Photo Flo Mixture. If you are setting up your own darkroom, contact a local photography store or darkroom or local officials to discuss safe disposal of the mixture and the fixative solution you will make to fix the strips upon completion.

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