I've been collecting the UK aerometric Duofolds in blue for a while now and have so far acquired a Slimfold, a Junior, a standard Duofold (which arrived this morning) and a Duofold Senior. I did some writing samples and took a picture of the pens to see if anyone else shared a love of them.
I also did a silly thing. These pens are very similar looking, and the Duofold and Duofold Senior are fairly similar in terms of breadth. I meant to fill the Duofold with Diamine Blue Black; instead I picked up the Senior, which was already quite full of Diamine Sherwood Green. In doing so, I ruined the end of a 30ml bottle of Blue Black and created an insipid sort of teal. I think I'm going to purchase four of the Cult Pens Deep Dark series to go with these pens as they work so well with dark colours.