This isn't a serious problem in need of a solution, but it has my
curiosity up. About 8 years ago, I used rubber bands (#33 whatever
that means) to attach cardboard tags to a dozen water valves to label
them. After installation, the rubber bands were not stretched. In
other words, they were stretched to get them around the valve handle,
but while sitting there for 8 years, they were not stretched. I
recently noticed quite a few of the tags were lying on the floor. When
I investigated, I found that the part of the rubber bands that were in
contact with the metal valves had turned dark brown and very
hard/brittle. The rest of each rubber band looked normal. I just
replaced all of them with new rubber bands from the same box that I
used 8 years ago. I imagine I should just get some twist ties or tie
wraps and use them in the future (if I am still around in another 8
years when they fail again).

I did some googling and found that UV light and cold can harm rubber,
but this location is inside and is in total darkness except for a few
hours a week at most. The room gets very humid in the summer and the
water flowing through the valves is from a water well. So, the valves
are often cooler than ambient and damp. In the winter, the temerature
can get as low as 40 degrees F in that room and the valves would then
be warmer than ambient (although not by very much). So, does anyone
know why the rubber got brittle?

Pat