The hilts of the two most common varieties of British cavalry swords (the 1796 Light Cavalry and 1796 Heavy cavalry patterns) were made of iron. Brass hilts seem to have been more fashionable in French swords, although these assessments are broad generalities. This is a period in which officers purchased their own equipment, which means that their swords were sometimes custom made (although many would have simply purchased a more decorated version of the same weapon used in their units). Prior to 1788, there were no standardized sword patterns in official Britsh military service, so the idea of having uniform sword patterns for the entire army was rather new. There was nothing stopping a British officer who wanted a brass-hilted sword from acquiring one, besides the possible expense. Examples of officer weapons from the 19th century range from engraved versions of the regular soldier's swords to highly ornate weapons with gilt inlays. The go-to reference for British military sword patterns is Robson's Swords of the British Army: The Regulation Patterns, 1788-1914. Perhaps /u/donaldfdraper would be able to help you with more specific discussion of French military sword patterns.