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Gas hypersensitisation, as you may know, is a method which was regularly used by astrophotographers. It included baking or soaking a film in a gas mixture, with this gas oftentimes being nitrogen.

As far as my understanding goes, gas hypersensitisation increases the film's effective sensitivity by diminishing reciprocity failure, while simultaneously decreasing film grain.

As film photography has started to die off to make room for digital photography starting from the turn of the century, the demand for hypersensitised film has apparently significantly died down as well, since I am unable to find any of such films for sale.

This person appears to have set up his own hypersensitisation apparatus, but this seems to be for personal use only. enter image description here

I wonder if there are still companies producing and selling gas-hypersensitised films, especially in (western) Europe. I am additionally interested in how much such films would cost, and how much they used to cost in the prime time of film photography.

  • "Bring out yer dead, I'm not dead yet" "As film photography has started to die off to make room for digital photography starting from the turn of the century" - Film did not "start to die off" to make room. Film use was severely reduced by the advent of digital but it was not making room for digital. While film use is not nearly what it was it once was it does not mean it is dying. There are new films being introduced, there are people still using film and more importantly there are young people learning film photography. "The news of my death has been greatly exaggerated" – Alaska Man Oct 8 at 17:24
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    @AlaskaMan "...you'll be stone dead in a moment". Five hipsters still clinging to a few photographic plates is not evidence that film is alive and well. 35mm roll sales have dropped like 99% since the peak two decades ago. This isn't to say that going against the grain and incorporating film into your work is a bad idea, but let's not be in denial about the facts. – J... Oct 8 at 19:44
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I think half of this question can be half answered fairly easily (so this is a quarter of an answer).

People making very long exposures on film needed to hypersensitize their film to deal with reciprocity failure. Those people were almost exclusively astronomers. None of those people will be using film now, and certainly any observatory with the financial means to hypersensitize film will be spending their money on improving their digital sensors instead, so whatever processes and suppliers they had will no longer be supplying either hypersensitized film/plates or the equipment to make them.

So, no, there will be no companies producing hypersensitized film or the equipment to produce it, as the market has entirely vanished. [This is the bit of the answer I am confident in.]

If you wanted hypersensitized film now (presumably because you want to do retro astronomy, like the person who you reference) then the cost of it would be the cost of setting up your own system to hypersensitize film. If you're lucky you might be able to acquire equipment cheaply from observatories which used to do this.

I don't know what it used to cost: I imagine it was never cheap.

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We used to experiment with a kind of gas hyper-sensitization using mercury. It wasn't the epitome of environmental concern but we were young, stupid, and irresponsible.

We would put a drop of mercury into a closed container with film and put it onto a room radiator to warm up and vapourize the mercury for varying amounts of time. This increased the effective speed which we then "rated" for shooting at night.

Alternatively, in a different direction, super-cooling of the film had its speed increases, too.

Fun. Good luck.

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In the distant past, gas-hypersensitization was practiced by most every major astronomical observatory along with cold packs to freeze film. These methods increase the film's ISO mainly by mitigating reciprocity failure. This is the demon that robs film of its sensitivity when long exposure times are required. Most observatories had their own equipment along with a person who specialized in this art. Also, film manufacturers hypersensitized some types of their slower films to create a film with elevated ISO.

  • Thanks Alan, but this does not answer my actual question. – timvrhn Oct 8 at 14:14
  • Alan, out of experience, do you perhaps know the price range of a hypersensitised roll back in the days? – timvrhn Oct 9 at 7:23

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