Protective Coatings – Anti-Corrosive Pigment in Primers When specifying a primer to inhibit corrosion on steel, which pigment has been traditionally used for strong anti-corrosive performance (historically in metal primers)?

Introduction:
Corrosion control on steel often begins with a primer pigmented to inhibit rust. This question verifies recognition of the classic anti-corrosive pigment historically used in heavy duty primers and shop coats for ferrous substrates.

Given Data / Assumptions:

• Substrate: steel or cast iron components.
• Coating: primer layer requiring active inhibition.
• Pigment choices: several common white and filler pigments plus one anti-corrosive pigment.

Concept / Approach:

Red lead (minium) has been widely used in traditional primers for steel due to its inhibitive action. Although modern health and environmental regulations encourage alternative systems, the conceptual answer in materials engineering remains red lead as the classic inhibitor.

Step-by-Step Solution:

Verification / Alternative check:

Old bridge maintenance manuals and shop primer specifications cite red lead primer systems before the shift to zinc rich primers and epoxy technologies.

Why Other Options Are Wrong:

Zinc white: primarily a white pigment. Gypsum: extender/filler. White lead: general purpose with toxicity issues, not the standard corrosion inhibitor for steel. Ferrous oxide as listed is not the standard inhibitive choice.

Common Pitfalls:

Confusing any oxide pigment with inhibitive pigments; overlooking historical context versus modern alternatives like zinc rich primers.

Final Answer:

Red lead (minium) for anti-corrosion priming