Humidity is bad for cameras. In 2009, I wrongly assumed that my Canon EF 300mm f4L lens was waterproof and used it in the rain. I got the photo, then some condensation inside the lens and fungus within a few days. Lesson learned: not all L series lenses are sealed. We can avoid the rain but still face humidity problems in storage. Desiccants are widely used in industry to lower humidity in packaging and we should use them in our camera bags too. I have recently changed from desiccant sachets to canisters.
Silica gel desiccant
Silica Gel is a common, inexpensive desiccant. It performs best at room temperatures (20 to 30 C) and high humidity (60 to 90% RH). Equilibrium humidity can be as low as 40% RH. Under 50% RH is sufficient to prevent fungus growth and corrosion.
A rule of thumb for sealed packages is 1.7 grams of Silica Gel for every 10 L of volume. In camera bags, humid air is repeatedly introduced and we need more silica gel and need to change it often.
Indicating Silica Gel has been washed with Cobalt Chloride. It is blue when dry and turns pink when saturated. There is also orange Indicating Silica Gel, which is approved non-toxic. Silica gel releases adsorbed water when heated and can be reactivated
I purchased 500 g of Silica gel in 25 g sachets on Ebay. The desiccant contains a fraction of blue indicating beads. The bags are made from Tyvek, a semi-transparent, breathable but non-dusting polyethylene material.
DIY desiccant canisters
You can buy desiccant canisters, which are simply expensive repackaged desiccant. I decided to make my own and used old photographic film containers. Each holds about 50 g of Silica Gel. The containers are semi-transparent, to see the indicating beads. They have sealing lids, to keep the desiccant dry until ready to be used.
The active desiccant canister has a perforated lid. I used a hot needle, heated over a gas burner, to make fine holes in the plastic. I then glued a piece of Tyvek to the inside the lid, to block dust. Take care not to plug the perforations! When changing desiccant, I swap the perforated lid from the spent canister to a fresh canister.
Recycling Silica Gel
To recycle Silica Gel, I use an oven at around 120 degrees C. Too hot and the indicating dye will deteriorate. There is a microwave method but I found that rapid heating discolours and cracks the desiccant beads. Here’s what I do:
- Empty the canisters onto a Pyrex dish and place in an oven around 120 C, until all indicating beads turn blue.
- Continue heating another 20 to 30 minutes, just to be sure, and then turn off the oven.
- Leave the desiccant inside the oven to cool for about 30 minutes. Do not open the oven, which would allow humid air inside.
- Transfer the still warm desiccant to sealed containers. It should not melt plastic.
I have also been successful in recycling Tyvek satchels. Be careful though: Tyvek melts at 121 C.
Desiccant canister performance
I first used my home made desiccant canisters on a month long trip to Indonesia in December 2009. This was during the monsoon and the weather was hot and humid. My camera bag was a Lowepro DZ100 waterproof backpack, capacity approximately 13 L. I used five 50 g canisters in one month, which is roughly one per week.
I have tried Humidity Indicating Cards to measure the humidity inside my bag and found that they are too sensitive. They are not suitable for packages that are opened frequently.