Complex sentence: However, steel flex nibs on fountain pens are rare; flex nibs required a considerable investment of skill to make, and the steel nibs of the time had poor resistance to corrosion from (often acidic) contemporaneous inks.
Split into simpler sentences: However, steel flex nibs on fountain pens are rare. Flex nibs required a considerable investment of skill to make, and the steel nibs of the time had poor resistance to corrosion from (often acidic) contemporaneous inks.