This big pen ( with a #416 in the midlle just to compare the sizes) ) was made for the first time in 1902. It seems that due to it's size it was only made by customer order . It is a very impressive pen!
This photo was worked on by my friend João Pavão Martins to whom I wish to thank.
After tis post I received this email from George Kovalenko a very well know collector and vintage fountain pen expert to whom I wish to thank his collaboration:
Concerning your RHR #420 Waterman's with sterling silver filigree:
Gorgeous pen, by the way. And congrats. But let me raise a few issues with your blog post.
You say it has an overlay, but the better name for it would be a filigree. Overlays are solid, and filigrees are pierced with openings.
You also say that the pen "was made for the first time in 1902". Where did you get that date?
First of all, Waterman did not make RHR pens until at least 1906-07. I will post something about this issue on L&P tomorrow in a new thread.
Second, the Art Nouveau filigree came in two styles, which were very similar. The first onewas completely asymmetrical, including the indicia, and may have appeared as early as 1902. It also had a slightly rounded cap top. The second one was asymmetrical only in the vine filigree, and the indicia is placed and framed by the vines symmetrically. The cap top on this one has a slightly domed top with a squared edge. This type didn't appear until late 1907, or early 1908. Your pen has the second type of filigree.
And lastly, as late as 1897, Waterman still had only nib sizes #2 to #6. The #7 & #8 didn't make their first appearance until 1907, and the #10 nib didn't appear until about 1910-11. So your pen must date from at least this period, or after.