Zinc Plating Either a bright or dull finish is acceptable. Bright zinc plating closely resembles bright chromium. However, bright zinc does not have the permanence of surface appearance. Zinc coated steel will not rust even when exposed by scratches because of the sacrificial protection of the zinc. On weathering, zinc turns to a drab gray color. Zinc should be deposited directly on the base metal (Nickel is permissible undercoat if base metal is a corrosion resisting steel). Parts having a hardness greater than approx. Rc-33 must be given a heat treatment prior to plating. Parts having a hardness over approx. Rc-39 must be given an after plating baking at 375ºF + 25º F for 3 hours within 4 hours after plating.
Spec.	Thickness	Comment
ASTMB633-98 e1
Fe/Zn25 SC4 (very severe)	.0010"
FE/Zn12 SC3 (severe)	.00050"
Fe/Zn8 SC2 (moderate)	.00030"
Fe/Zn5 SC1 (mild)	.00020
Type I		Without supplementary treatment.
Type II		With supplementary chromate treatment.
Type III		With supplementary colorless chromate treatment.
Type IV		With phosphate conversion treatment.
		Corrosion resistance requirements: Type II - 96 hours Type III - 12 hours