Assertion: fountain pen's ink | /r/HasProperty | designed for the pen
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text: Pen manufacturers using a proprietary cartridge (which in almost all cases are the more expensive ones like the ones mentioned above) tend to discourage the use of cheaper internationally standardised short/long cartridges or adaptations thereof due to their variance in ink quality in the cartridges which may not offer as much performance, or be of lesser quality than the manufacturer of the pen; ink that has been designed specifically for the pen.