What is the maximum humidity you should store coins at? I know the generic answer would be as low as possible. But just curious if anybody really knows what's acceptable. Is anybody else paying close attention to this? I run a dehumidifier to maintain 60% room humidity. If I set it much lower, it would run constantly. Then I use large rechargeable, silica gel bags to dehumidify smaller sized storage areas. (Temps are constant.) At best I can maintain my storage location around 25% for short periods, but usually climbs to 50% in a relatively short amount of time. I don't mind recharging silica gel packs every 6 months. I don't want to have to do it every month. This isn't the coast but it's not the Rockies either. We have a decent amount of humidity to deal with for a good 3/4ths of the year. I also wonder if it would be better to not go so low for when you do want to take stuff out. For example an album needs to be pulled out to fill a hole. When its very low, and you bring something out into the normal air, you can feel slight condensation on the albums, materials, etc... FWIW, I do intend to have a better set up 4 to 5 years from now.
The upper midwest can be pretty brutal on coins. Not as bad as the deep south, but bad. I wouldn't stress too much unless I was storing these in the basement. ON the first or second floor it sounds as if what you are doing is good enough. Non-pvc plastic, some humidity control, and silica that you recharge occasionally. Also try to run the central AC whenever the temp calls for it, as its one big dehumidifier. If you ARE storing in the basement, at least April-Oct I would run your dehumidifier nearly constantly, letting it drain automatically into a drain if possible to make it easy on you. Chris
As you say, "as low as possible" for metallic coins and medals". Since they will be exposed to home humidity when being shown or worked, you can reduce the time they face this by keeping them in a zip lock freezer bag ( double seal are tighter) with a small silica gel pack. Squeeze all the air out possible and then the silica gel will have very little work to do and will not require recharging often. I have experimented with the "vacuum zip bags" in the same situation, and I find no difference, and the regular zip lock bags can be found ( Walmart I think ) in sizes large enough for albums. I use the largeest zip lock bags to freeze 2 half gallon cartons of low fat egg nog at a time.The stores only have it here for the 2 month holiday season, so I freeze and get one out when the urge hits in the hot months of summer. Jim
I would probably shoot for 40%. You will find this difficult to achieve for whole room living areas because there is just too much air exchange, and you would be surprised how much moisture you yourself will put into the air just through respiration and evaporation. But if you create sealed micro environments as in tupperware storage containers or ziplock bags with silica gel you should be able to get down to that level and maintain it for a long time between recharges of the silica as long as you are not opening and closing the containers all the time. (If you are storing paper collectibles such as paper money they require a higher humidity level lest they dry out and become brittle. But separate micro environment containers with different humidity levels can be stored in the same location. If you have materials that are truly moisture sensitive such as steel or possibly copper I would shoot for even lower levels if I could.
Numbers vary depending on where you look but the Navy tries for around 30% in mothballed ships. The problem with moisture is that it accelerates chemical reactions. If you're keeping sulfur-containing gases away, then you don't need to stress out as much about humidity.
