Metal-coated crystals is a Earth technique of coating the crystal surface with metal giving them an metallic sheen. Crystals treated this way are use as gemstones and for other decorative purposes. Coatings include gold, indium, titanium, niobium, and copper.
This technique has become found among as a type of practice for some Jedi and some Sith; although, the treatment says to be a challenging effort, therefore, the effort has found rare use but proven to be quite effective. Jedi, especially those from Earth, would coated their lightsaber crystals in the metal coating of their choosing. This could either enhance, or alter the crystal's abilities depending the type of crystal being used.
Lightsaber crystals coated in titanium for example have been known to produce blades that are sharper looking, and are able to cut through metal much easier than the standard blade.
Some metal coating such as iron, have cause the blade to be heavier than standard, but can be effective to penetrate defense with proper training.
One such coating that is rare, but has proven to be the most unique among the coating is the use beskar ore AKA Mandalorian iron. When coated to a lightsaber crystal properly, they produce a blade whole lot stronger than the standard, and they been known to challenge the Sith's synthetic lightsaber crystal's rare ability to break another lightsaber blade. A beskar coated crystal is the only known coated lightsaber crystal to able to cut through Mandalorian iron armor.
Trivia[]
Metal-coated crystal is a real thing: https://en.wikipedia.org/wiki/Metal-coated_crystal