In a specific example, the concentration of copper salts in the film is at least about 0.1 mole/liter, more preferably at least about 0.25 mole/liter, and most preferably at least about 0.5 mole/liter (up to the solubility limit of the metal ion in the solvent). [0061] Another component that may be added to the viscous liquid film may be a surface agent such as a wetting agent, a brightening agent