Just yesterday I was in the process of cleaning and re-moisturizing a 70 year old glove and an old problem emerged that of the yucky green stuff on brass grommets on many old gloves. I think all the old brass grommets were susceptible to the formation of this process which results in the formation of verdigris (look it up on the internet) on the brass.
"Verdigris is the common name for a green pigment obtained through the application of acetic acid to copper plates or the natural patina formed when copper, brass or bronze is weathered and exposed to air or seawater over a period of time. It is usually a basic copper carbonate, but near the sea will be a basic copper chloride. If acetic acid is present at the time of weathering, it may consist of copper(II) acetate."
Verdigris was actually used as a paint pigment by very early artists.
Verdigris is a problem attuned to guns and holster collectors in that when brass cartridges are kept in leather belts for long, this process can begin to take place, so collectors won't put the cartridges into
their leather loops for long time or, if they do, they clean their cartridges every so often. The writeup I read here, which we're all familiar with is that leather attracts moisture, leading to the development of the reaction to the brass.
I would recommend, if you want to combat this problem that you read about this chemical process. Cleaning might present some hazards so be sure and research this and clean your hands after working on this green "sludge". Recommend using rubber gloves.
I've found two things that will "work on" or help clean this verdigris. One is common rubbing alcohol, which seems to work faster or "Goo Gone" product. You have to be careful because you don't want to stain your surrounding leather. I use a q-tip and apply it to the metal part carefully. Some of the verdigris works under the leather lacing, so you have to make sure that you can get underneath the lacing.
REMEMBER it appears that this verdigris weakens the old lacing, so be careful not to pop the old lace.