I remember seeing in recent years a rough humidity gauge that was made by laminating two different woods together that had different expansions due to humidity, similar to the way a bimetallic thermostat works.
If anyone has a pointer, that would be appreciated. I tried to find this using the online index search, but I could not come up with the right search terms, I guess. Searching for “wood humidity” found hundreds of matches!
Replies
https://www.instructables.com/Humidity-Gauge-Made-Out-of-Wood/
I'm pretty sure Fine Woodworking had an article, way back in the day. They might have called it Thomas Jefferson's hygrometer?
Bruce Hoadley described a similar device, called a "widget," in his book.
Hoadley, R. Bruce. "Understanding Wood." Taunton Press, 1980, p 94.
There is a 2nd edition of this book but I do not know if the "widget" is covered.
The FWW version was similar to the one at Instructables, but it used two different wood species, instead of two different cuts (long grain, short grain). Maybe the FWW also had different cuts, as well as different species. I remember that is was near the end of an issue; probably an inset box in a different article. (A pointer to the FWW one would still be appreciated!) The Hoadley one magnifies the changes of the width of one block of wood.
I'm not sure why the "low tech" nature of these gauges appeals to me, over using a proper sensor. Now I have additional ideas to play with. Thanks for the replies.
A few years ago, I built the Rittenhouse hygrometer that you may be asking about. The inventor was David Rittenhouse, who was a scientist/inventor and friend/colleague of Thomas Jefferson. He used a cross-grain lamination of mahogany for the pointer (he didn't use two different woods). If you search online, I'm sure you will find information about it.
I have mine located in my shop, next to an electronic hygrometer, which I used to calibrate my wooden hygrometer. Over the course of a year, I penciled marks on the wooden hygrometer to indicate what the electronic one read. I look at it from time to time, and the two have matched quite closely over the past few years.
I think it also appears in one of Roy Underhill's books.