Pure Zinc Layer
"Pure zinc layer" refers in metallurgy as the layer at the top of the surface of hot-dip galvanized coating which only (>98%) contains Zinc. The pure zinc layer has a dense and complex hexagonal structure, and is soft, tough, and ductile, making it difficult to break down when processed. This helps with workability of galvanized material and avoids "peeling off" of galvanized surface coating.
Including the "pure zinc layer," also known as the η (Eta) layer, hot dip galvanizing coatings consist of at least three distinguishable layers, the other ones being the δ1 (Delta one) layer, which is a dense mixture of iron and zinc and has tough and ductile properties, and the ζ (Zeta) layer, which has a columnar structure and is relatively hard and resistant to wear. Since all layers below the pure zinc layer contain iron (Fe), with an increasing amount the deeper you go, they are prone to corrode faster and produce red rust.
Reference: Abrasion Resistance of Hot Dip Galvanizing (Galvanizeit.org)
Cross-sectional structure of galvanizing layer