Just recently ordered a vintage German pen from the 30's on the Bay. (FYI, it was a BIN). The ad says it was completely and professionally restored. The image shows a cork "gasket" in the ink window. Questions: Do I need to avoid specific inks because of any caustic/destructive nature?What inks are considered more "gentle", especially toward vintage pens?Would (brightly?) colored inks be more inclined to cause problems?Would I be better staying with the black/blue/blue black inks?What brands might be better to consider? Will post a picture of the pen when it arrives from the Netherlands - around 6/18. Thanks for you help and insights.