The large "dome-shaped" items are not buttons, unless they have shanks
on the back. They are all beautiful, none-the-less. I recommend you join
Buttonbytes on Facebook or Google groups to get long-time collectors'
opinions.
It is hard to say what kind of shell that is from the photos, but we
generally know that buttons from freshwater mussel shells were used to
make less elegant and more utilitarian buttons. During the mid and late
19th century, the discovery of abundan...
The thingie you mentioned is called a shank. Do yourself a favor and
join the National Button Society. And then look at your state listed to
find a local button club you can join. The NBS have been around since
the 1940s and are the biggest repositor...
There are numerous sites on Facebook that you can join and get almost
immediate answers to your questions about buttons. Ex: Illinois State
Button Society, Buttonbytes. Someone there can probably answer your
question.