A silver nanoparticle composite or a copper nanoparticle composite is formed in which the silver nanoparticle composite has silver nanoparticles, and both (a) one or more polymers and ascorbic acid adsorbed on the silver nanoparticles, wherein the (a) one or more polymers are selected from one or more of cellulose acetate, cellulose acetate phthalate, cellulose acetate butyrate, cellulose acetate propionate, cellulose acetate trimellitate, hydroxypropylmethyl cellulose phthalate, methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, hydroxypropylmethyl cellulose, and carboxymethyl cellulose. Copper nanoparticle composite are similarly formed in which both the (a) one or more polymers and ascorbic acid are adsorbed on the copper nanoparticles.