Under perfect conditions they are o.k. for the long term, but in real life conditions they get spotty, dingy, do not retain the enamel markings very well, and lose them with cleaning attempts. Watch producers put silver dials on their best pocket and wrist watches. Exception being r.r. watches that had to survive coal gas environment, needed best visibility and permanence. For metal dials my favorites for fine watches are multicolor gold, platinum and gold, gold alloy, and good enamel paint jobs. Also never saw a bad copper metal dial; not sure of their composition. Photos here of each. The pentagon is 100+ years of oxidation on solid gold alloy. Fairly common English multicolor gold. Illinois is solid gold with fired white ceramic, Elgin platinum with gold plating, 1932 copper, 1940+ black enamel.