The greater the contamination of a stainless-steel weld, of the bead after the weld?

• A. The whiter the color
• B. The lighter the color
• C. The darker the color
• D. The redder the color

Answer: (C)

Contamination on stainless steel surfaces causes extra oxidation when heated. Stainless steel relies on a thin chromium-rich oxide layer to stay bright and corrosion-resistant. When the surface is contaminated, oxide builds up more thickly as the weld heat drives reactions, so the bead develops a darker, duller appearance. The more contamination there is, the thicker the oxide layer becomes, and the bead color shifts toward dark tones. Lighter or white discoloration would imply less oxidation and cleaner metal, while a redder tint usually relates to different heating conditions rather than contamination level. So the bead darkens as contamination increases.