Verdigris forming around a machine screw secured with PVAc (Polyvinyl acetate)
I made this small brass hammer a couple of years ago. One face is brass, and the other a removable piece of horse butt leather. When recently unscrewing the face, I was surprised to find verdigris forming. But it makes sense: the acedic acid offgassing from the PVAc (Jade 403) must have reacted with the copper content in the brass. It you want to make verdigris, this might be a good thing: if you are working on a book with brass or bronze hardware, PVAc should be used with caution.
The brass face of this small hammer is useful for flattening joins when working with a grainy leather, like goat. If the face is dinged up and dented, it tends to match the leather better than a smooth, clean face, which flattens the leather unnaturally. A second caution: sometimes a dented, irregularly shaped tool may function better than one that is cleaned up and made geometrically perfect. Try it out before you clean it up.