Another look at the "salt test" for calibrating cigar humidor hygrometers

One cogent piece of advice that's given with regard to properly calibrating hygrometers for cigar humidors is the use of the "salt test." Without getting into the science behind why it works, the test is designed to produce 75% RH in a controlled environment. For those of you who haven't discovered this by now, here's the recipe:

Ingredients: Table salt, a clear, Ziploc-type sandwich bag, a soda bottle cap (or other small container), distilled water, hygrometer.

Place about a teaspoon of salt in the bottle cap and drip just enough distilled water on the salt to get it wet. If done right, it should have a thick, pasty consistency, not watery. Place the cap and the hygrometer face-up in the baggie, so you can read it.

Seal the baggie, but leave a little air inside, and let it sit for at least 6 hours. By that time, the hygrometer should read exactly 75%. Whatever number it's off by, just use the calibration screw on the back of the unit to adjust it accordingly.
So why do I bring this up? Well, I recently received an email from my good friend Bill W., a civilian engineer with the U.S. Army, who had this to say about the salt test:

"After over forty years of smoking cigars and over thirty years of working in calibration labs, although the "salt test" is a perfectly valid procedure to verify a hydrometers reading, it should ONLY be used on analog hygrometers. The electronics in digital hydrometers cannot stand up to the highly corrosive atmosphere the test creates. (It eventually affects analog units over time, too.) The Reference Level has standards, but they are expensive and require training to use and read correctly. I would suggest using a Boveda Calibrating Pack. For about five bucks the average user can not get an easier to use or more accurate standard. It also takes the guess work out of the salt test for those who maybe new to it, and it's a lot less messy."

Your thoughts?

~ Gary Korb


Anonymous said…
Thank you and your friend Bill W. This info just kept me from ruining some digital hygrometers.
MarkC said…
Hmmm. I wish I'd read this four hours ago...
Anonymous said…
Not like you're going to leave it in there permanently. A few hours isnt going to hurt the hygro
There's an easy solution: calibrate an analog hygrometer using the salt test. Then place both analog and digital hygrometers in your humidor for a few hours, then calibrate the digital until it matches the analog.
Anonymous said…
Realizing this post is 5~ years old I've been trying to find an answer to whether the salt used must be iodized 'table' salt. Anyone know for certain?

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