This is a Merz & Krell piston fill pen in gray snakeskin celluloid from the 1950s. It is similar to celluloids used by several European brands in the 1940s. It has a large ink view window in the barrel with a black and clear spiral pattern and if you look closely you can see the piston seal in the window. The piston knob is accessed by removing the black end cap. The nib is a lightly gold plated Number 2 stainless steel semi flex and this example has more plating than most. There are no makers marks on the 4 13/16 inch long pen other than a half eclipsed sun stamping on the nib.