These are one of the least well documented items made by Esterbrook.
I will try to collect here as much information as possible. Of course the interested reader should always consult Brian's (and Lisa's :)) website www.esterbrook.net (start from http://www.esterbrook.net/relief.shtml)
Can this be the earliest Relief pen?
American agriculturist: Volume 48 - Page 590, 1899.
1913 (British Books in Print)Eyedropper Relief. I have not been able to find the full photo yet. The imprint does say "Gold Relief". So the pen is the Onoto eyedropper shown by Brian in http://www.esterbrook.net/relief3142.shtml
Hazell's Annual (1915)
Level filler(?) Relief.
If you reached this page, chances are that you are interested in the history of fountain pens. Patents offer an interesting insight for the history of our beloved pens. You should consider purchasing George Kovalenko's book on Fountain Pen Patents 1911-1950s. Click here for more information. This is a labor of love and is the most comprehensive collection of pen patents that exists. George works currently on the first volume, which I am waiting anxiously for.