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How much grams of silica gel should I put for my 4.6L air tight dry box? I have a silica gel inside of a plastic sachet but I cut the plastic and put it in a small open container to absorb moisture more effectively. Any suggestions how much should I put?

  • I usually just use a few packets, but don't know how much that is or whether it is sufficient. You also need to make sure that the gel is still able to absorb moisture. To "recharge" it, just heat it a bit. – xiota Dec 29 '18 at 8:26
  • vtc b/c This is a non-photographic chemistry question. See chemistry.SE: Hygroscopic material absorption level. – xiota Dec 29 '18 at 14:05
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    You can always just get a humidity meter and then you can tell if you put in enough or not. Basic ones start at maybe $10. Note that the basic ones won't read below ~15% RH. – Daniel Kiracofe Dec 29 '18 at 15:37
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    It's of practical value to photographer's that have to take their gear out in cold weather. Even if the humidity in a home is low (30%) or so, if the temperature drops a lot there can be condensation inside the camera/lens. So, for that sort of usage, dry boxes can save a lot of shots. – doug Dec 29 '18 at 19:05
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A 5 liter container will have about .1g of water at 100% humidity at room temperature.

Each time you open the container most of the air in it will mix with room air. If your environment is 80% humid then the silica gel will adsorb about .08g of the water. Silica gel saturates at about 40% of its weight but to keep things dry you should limit it to 10% or less.

So, for your box, 10g of silica gel will keep things quite dry for about 15 openings or so. More if your room averages 50% humidity, less if it's really humid. You can re-use silica gel by heating it at 250F for a few hours which drives most of the water out.

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