Examples of suitable acidic second materials include, but are not limited to, polymeric acidic materials such as polyacrylic acid, polymaleic acid, carboxymethyl cellulose, alginic acid, polyaspartic acid, and polyglutamic acid; organic acidic materials such as aliphatic and aromatic acids; and inorganic acids such as metallic oxides, such as aluminum oxide; and salts such as iron chloride.