I use archival calligraphy ink and a cheap calligraphy pen. I like white ink on osage because the darker the osage gets, the more the lettering stands out.
Here is my lifetime supply of ink and my pen. Hard to read but the ink is Speedball Super Pigmented acrylic.
I have found the points wear out pretty quickly. To make neat lettering the point has to be replaced as soon as it starts chattering across the wood surface. If you go this route, buy the finest tip they sell at the craft store. I get my stuff at Hobby Lobby.