KKay, there are a range of Esterbrook nibs all in some flavor of medium. What does the nib actually say on it? Is there a number, and if so, what? That will give people some idea as to not only what grade (1xxx series, etc.) it is but also details such as if it's a manifold (i.e., extra rigid) for using with carbon copies, an oblique nib, or what. There are also some late nibs (which may be Venus or Osmiroid nibs) which do just say "Medium".
I only have a couple of LJs and they aren't copper . One is black and the other is grey mackerel. I got the the grey one off eBay a few years ago along with another grey mackerel, both of which had 9xxx series nibs for a really good price. Possibly because the auction ended at around 11 AM EST on a Sunday..... . Didn't fare quite so well with the black LJ, but it had a 9284 Signature stub on it (it's also called a music nib in some stuff I've seen, although it's not a true music nib in that it doesn't have three tines).
Black Esties are boring, but at this point I'm looking for specific nibs. I have all the 9xxx nibs at this point except for a couple of relatively uncommon/rare ones that tend to be really expensive.
Ruth Morrisson aka inkstainedruth
"It's very nice, but frankly, when I signed that list for a P-51, what I had in mind was a fountain pen."