Introduction: Silver, prized throughout history for its luster and shine, develops a black Ag 2 S tarnish layer that is aesthetically displeasing when exposed to atmospheric pollutants. Tarnishing, and subsequent polishing, leads to irreversible material loss and object damage. Currently, nitrocellulose coatings are often used to prevent silver from tarnishing, however non-uniform coatings and degradation over time limit their effectiveness. Atomic layer deposition (ALD) has been explored as a new method for creating dense, uniform, and conformal coatings on 3-dimensional (3D) objects that are more effective than nitrocellulose in preventing silver from tarnishing. Results:To create high quality ALD coatings on 3D objects, slowing down the ALD process is critical to ensure proper precursor exposure. Non-ideal deposition of organo-oxy-metallic compounds can occur with fast deposition rates that do not allow sufficient flow around 3D objects. The coatings can be removed by dissolving the Al 2 O 3 ALD films in aqueous NaOH. Thicker ALD films prevent defects from occurring on non-ideal surfaces and effectively prevent silver objects from tarnishing under ambient aging conditions. Conclusion:Thick ALD films, deposited with sufficiently long precursor pulse and purge times, may be effective in preventing complex, 3D non-mixed media silver cultural heritage objects from tarnishing.

In this article we report on the characterization of atomic layer deposited (ALD) films on silver alloy objects, both with regard to film porosity, which potentially limits their effectiveness as tarnish barriers, and with regard to color change upon deposition, which affects their visual appearance. We find that the porosity of ALD alumina films decreases with thickness, and shows no clear dependence on surface preparation, nor on multiple ALD oxide layering. We also find that the optimized structures for minimizing color change are sensitive to the composition of the alloy, and must be tuned accordingly.

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