I have recently found a fountain Parker pen my dad gave me years ago. I decided today I wanted to know what model my pen was and a little bit about it or if there is any history. Since searching the Internet the closest thing I can find is a limited edition blue marble centennial pen however I wondered if anyone could help identify the pen and conferm my guess or not. I have two of the pens both are fountain and have screw caps. I would also like to know why one of the nibs has become discoloured and if there is anything I can do. Thank you and any advise is much appreciated