Saratogadriver, that master ink bottle looks exactly like it - good eye!But I checked Ed & Lucy's Ink book, and it says the DIAMOND & ONYX bottle only comes in 5.5" and 7" sizes, so I'm not yet ready to declare success.
I saw a photo of a bottle that looked just like it that was embossed "TWIN CITY MFG CO, NORFOLK VA". But that company bottled vinegar, syrup, bluing, and maybe other stuff too. Then I found this in a 1920 Illinois glass company catalog from 1920. The "ROUND EXTRACTS" bottle on the bottom right appears to be the mystery bottle. So I guess the answer is that it was a generic style of bottle that could have held almost anything.