Never mind the free machining video - what was that pen!!
Righty ho then peeps! It seems the pen was more interesting than the video :) Congratulations to the lady who watched it 8 times to try and find out the make.
Yes, it is an Indian Ink, waterproof pen, with a soft tip which is a bit like a paintbrush but writes well. It's a Faber-Castell, Pitt artist pen and is size B. Sorry, I can't remember where I got it but it must be widely available or I wouldn't have found it.