Hydrogen Hypering of film

Caution : Hydrogen is very dangerous. Care must be taken when using hydrogen to avoid any sparks or open flames. Hydrogen burns with a flame that invisible to the human eye. This is one of the things that makes it so dangerous.

Hypersensitisation is the process of treating a film with some chemical agent in order to incresa its effective speed during very long exposures.

Colour films must be hypersensitised in forming gas to avoid changes in
colour balance due to crossover. Crossover occurs because different layers increase their sensitivity at different rates when pure hydrogen is used. A similar effect is observed in long exposures with unsensitised film due to different rates of reciprocity failure occurring in different colour layers.

Colour balance shift is not a problem with monochrome film. When comet Hyakutake appeared in our night skies, I needed to hypersensitise some film fast. I decided to use HP5 as my film. The reason was practical. I had a bulk roll of HP5. It was fast enough to allow me to take quick exposures and sufficiently fine grained to allow a 12x16" enlargement. My RA drive Dec drive and guidescope were not fantastic and I would have difficulty guiding long exposures while contending with a lot of proper motion.

I had some basic starting points and I remembered talking to some astronomers using the 26" Upsala Schmidt camera at Siding Spring Observatory who were using pure Hydrogen gas for 4 hrs at an elevated temperature on Kodak 2415.

To cut a long story short I hypered strips of HP5 for 1,2,4 & 8 hours. The strips were in a daylight developing tank placed inside a lab desiccator. I processed these as detailed below :

Film HP5
Developer Ilford Plus 1:9 10 mins at 22 C

Agitation constant first 30s then 7s / 30s thereafter.

I took the processed stips along with an unsensitised control strip to a friend at Film & Sound Australia. He measured the density of each strip for me. I used the opportunity to calibrate my spotmeter as a densitometer. The hyper data data is presented in the table below and plotted in figure 2.




 Time in Hydrogen (Hours)

  Photographic Log Density units

 0

  0.44000

 2.0000

 0.52000

 4.0000

 0.61000

 8.0000

 0.75000

note : a change of D= 0.3 theoretically equiv to one stop.
Just for interest, when D changes 0.17 actually equivalent to one stop enlarger exposure ie one zone.

Summary

Place silica gel in the base. Place film in a daylight tank inside the desiccator. Use whatever pump you have to pump on the film and desiccant for a few hours. Do this in a room with subdued light. My first attempt was spoiled because the film tank leaked light over the extended period of pumping & hypering in a brightly lit room.

For Ilford HP5, use 100 % H2 for 4 hrs at room temperature.
Process in Ilford Plus 1:9 10 mins at 22 C

Agitate continuously for the first 30s then 7s per 30s thereafter.

At some point, I'll repeat the procedure for 2415 & put the results on the site.

 

¦ Insert photograph of Comet Hyakutake here.

 

 

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