The anisotropic dimensional properties of ivory have been investigated under varied temperature and relative humidity conditions. Migration of moisture into and out of ivory was found to play the principal role in its expansion and contraction. To control the resultant swelling and shrinking, the use of polymer coatings and waxes to act as moisture barriers was examined. A particularly effective polyvinylidene chloride emulsion was further tested for facility of application and aesthetic appearance. The incorporation of plasticizers into ivory to reduce brittleness and thereby stress was also investigated.
https://www.iiconservation.org/node/548
A high-performance aqueous PVDC (polyvinylidene chloride) emulsion that, on drying, forms a thin film characterized by high barrier to oxygen and other gases and to water vapor, together with outstanding heat- and radiofrequency-seal properties, flame retardance, and oil and chemical resistance.
http://www.asahi-kasei.co.jp/chemicals/en/specialty/page01.html