What is the optimal humidity level?

Does anyone know what the ideal level of humidity is to protect coins from toning or corrosion?

I keep my coins in a safe that is fairly air-tight. I use two Eva-dry renewable dehumidifiers (the kind you plug in to recharge). Each of them is supposed to cover 500 cubic feet. The safe is only 30 cubic feet and is located in a room that has a regular plug-in compressor-type dehumidifier set at 40%.

I recently found an inexpensive digital hygrometer (see photo) that was only $10 at Amazon.com. It shows the humidity level at 49-50% with the dehumidifiers fully charged. I'm surprised it isn't lower.

Do you think this is dry enough?

 

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The lower, the better!

 

0%

 

50% isn't terrible for coins but the lower the better, in general. In practical terms, 25-50% is probably the most reasonable target range.

 

I agree. I would imagine most coins that have been around for 100+ years weren't afforded near the consistant conditions people provide today.

 

50%rh is not good. That's what I have if I do nothing at all.

You're on the right track with the EvaDry. Get more of it. I run at 16-21%rh.

Also... You mentioned the room has a dehumidifier set to 40%rh. Why do you have 50% ?

 

If I am reading that correctly, the room is doing fine at 40%, but the safe is 49-50% (with the dehumidifiers fully charged). Dehumidifiers - plural while he has "a compressor-type dehumidifier" (singular) for the room.

 

Yes, that's how I read it.

Doesn't it seem odd that the safe interior (with fully charged EvaDrys) has worse humidity than ambient ?

 

I use 4 of them in my safe, and the only time the directions say to plug them in is when the view window shows the crystals are pinkish. This is the indication to plug them in. Leaving them plugged in all the time they get quite hot ... i dont know if they would burst, but i dont know if i would chance it.

just for clarification - in case there are multiple dehumidifiers with similar names, here is the item i am talking about

 

Yeah, a silica gel bag designed to dehumidify 33 Cu. Ft. works wonders in an enclosed 1 Cu. Ft space for quite a while. But I've never been able to achieve less than 25% even with a brand new one fresh out of the package.

When the hygrometer starts reading in the mid 40s, I recharge them in the oven. That's usually once or twice a year.

0% would be the most ideal.

 

they do get quite warm, but not enough to burn. I dont pretend to claim they are in any way better then the older style silica cells. I just liked being able to plug them in over night or so instead of running the over for a few hours lol my wife complains enosugh about them being plugged in ... dont need to tempt her with my running the over for that long :loud:

 

Anyone should be able to accomplish 10% or lower through the use of airtight sealed containers and lots of silica.

As you are aware, most safes are not airtight sealed containers.

 

The room is actually at 52% so the indicator on the dehumidifier may not be accurate. I'll try turning down the dehumidifier in the room to, say 30% and see what happens.

 

The Eva-dry units ARE silica gel. Are you suggesting that the plug-in cycle doesn't fully regenerate them? I usually leave them plugged in for 12-18 hours and the indicator is bright blue.

I have found the paper silica gel packs fall apart after a few regenerating cycles. I think the glue dries out.

I have others that are in metal canisters. I will try those and see if they work any better.

I agree with Daggarjon that heating in the oven is a pain and my wife complains also.

 

I haven't found an airtight container, yet.
Even using ziplock bags with silica gel inside, the color indicator turns pink after a while.

What do you use?

 

I have the same problem with the humidity in my storage area. I have 2 high capacity EDV500 Evadry dehumidifiers with one more currently on the way. My hydrometer stays between 47-50% humidity. I also have two small silica containers in the area as well. Can't seem to get below 45%. If anyone knows a secret...do share.

 

The safe may very well be a "paper or fireproof safe" which is designed to protect valuable personal papers and such and have walls of concrete or other moisture containing minerals that release water into the safe's cavity. Such material will absorb and release water to maintain a humidity similar to the air when opened. Silica gel will absorb the moisture in the safe, but over time the concrete/gypsum can release extra moisture.

Unfortunately most people can't afford the solid steel burglar safes, but buy the more readily available paper safes.

Silica gel should not be expected to remove water down to 0% , even when fully charged due to its chemical composition. If the humidity level in a sealed pill container went to 0%, the pills would probably be prone to breaking and time release components would not perform as designed.

Jim

 

If you are using a storage area such as a cabinet or closet, any small crack , or exposed surface, especially of wallboard or wood, will be exchanging moisture through it to the other areas of the home. Many houses are built on concrete slabs, and some of this may be exposed also. To fully control the exchange, all of the surfaces would have to be covered in acrylic or epoxy similar to the stuff for concrete garage floors.