Bottled ink is one of the joys conferred by fountain pen ownership. An enormous range of colours are available (you can even mix your own); it can be economical and eco-friendly; and there's some satisfaction in the process of filling a pen. It can of course be inconvenient at times, but the sheer variety of ink on sale in the 21st century is a testament to the ongoing popularity of bottled ink and the affection in which it is held.
Any fountain pen can use any reputable brand of ink - despite what pen manufacturers and their vested interests might imply. It's true that there are some pens that are more fussy about ink than others, and there is quite a wide variation in the viscosity and colour of the various brands, but in general the choice of ink will normally come down to personal preference or cost. However, two brands which stand out in most often in polls of fountain pen users are Waterman Ink and Diamine Ink and we heartily recommend these to any fountain pen owner. Diamine in particular offers an enormous range of colours and it's still manufactured right here in the UK.