found a bottle it seemed fine , then it cracked in 2

[Gene]

Usually temperature change is the issue. If I am bringing a bottle in from a cold environment, I wrap it up and let it acclimate slowly to the warmer temperature. If I am digging in warm weather, same deal-wrap it when it comes out of the hole. While washing, make sure the water is as close as possible to room temperature. Sometimes even with those precautions they crack. 1900-1925 era glass seems susceptible to this particularly. I believe that is the bottle from inside an old fire extinguisher.

I totally agree. I had to learn the hard way NOT to use hot water or even moderately hot when washing bottles. I had two nice ones that I dug with no appearances of any cracks and they both broke in half washing them in moderately hot water.