According to Mathur et al., "the modern fountain pen nib may be traced back to the original gold nib which had a tiny fragment of ruby attached to form the wear-point."Following the discovery of the platinum group of metals which include ruthenium, osmium and iridium, "a small quantity of iridium was isolated and used on the iridium-tipped gold dip pen nibs of the 1830s." Today, nibs are usually made of stainless steel or gold alloys, with the most popular gold content being 14 carat (58⅓%) and 18 carat (75%)^. Titanium is a less common metal used for making nibs. Gold is considered the optimum metal for its flexibility and its resistance to corrosion, although gold's corrosion resistance is less of an issue than in the past because of better stainless steel alloys and less corrosive inks.