erm, grease does go hard. exposed to oxygen and water the aromatic hydrocarbons in the carrier such as ethylene polymerise to plastic like structures. for the most part you want it to that as it helps bind the grease in place, but over the years this forms larger chain molecules that you don't want in a grease. the prevent the slip of platletes of moly or lithium or even teflon inside the carry which is why old greases feel hard and tend to have greater stiction. leave it in the tub and there is only a limited supply of oxygen for it to polymerise, open it to air and a layer will form on top that stops the reaction, but allow enough air and water to expose the surface and it will penertrate and continue the reaction.
or I'm lieing and just making shit up because it's friday. you choice.
milk is a good lubricant. but it doesn't displace water.
