I just got a gallon of Mobil DTE 25 (which I found out is described as
a hydraulic oil). Viscosity ISO 46. I wanted to use this on my 13"
south bend lathe. The oil came in a second hand container and on the
container a hand written warning states that this oil will corrode
brass.

I went to the mobil website and saw that they have a spec for copper
corrosion with a ASTM D 130 standard and they state that it has a "1B"
result. I went to the ASTM site and found out that the standard
requires you to immerse a copper strip in the test oil which is heated
to a certain temp for 3 hours and then the strip needs to be examined
for corrosion. However to find out what a test result of "1B" means,
but you have to purchase the active standard for $9.

Is "1B" a test result of no corrosion to copper? Will this oil be
harmful to copper and its alloys? Brass, bronze, monel? Just curious.

Aloha, Russell