Private Reserve Ink Essentials Empty Standard International Cartridges are an essential part of the fountain pen experience. Easy to use and ideal for traveling. Bring multiple colors in one convenient pack mess free. New to fountain pens or an expert? Filling and using cartridges will be a rewarding adventure. Standard International Cartridges – These cartridges can be used with all standard size pens and hold a larger amount of ink for longer or one color projects.