Providing High Quality Hot Dip Galvanized Coatings Since 1967

Galvanizing color appearances, from bright silver to dull gray

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We get calls periodically from fabricators or end users asking if they can request a certain color or shade in the galvanizing color. We also get calls from fabricators asking why their steel came out a certain color today, when the load they galvanized the week prior came out a different color. The truth of the matter is that the galvanizer has very little control over the exact finish color. Please let me explain.

The production of a galvanized coating has as its basis a metallurgical reaction between your steel and the molten zinc in our galvanizing bath. This reaction results in the formation of several iron-zinc alloy layers (dark), with normally a pure zinc outer layer (bright silver). Certain elements found in steel (mainly silicon, phosphorous, carbon, and manganese) can dramatically affect the alloying reaction between steel and molten zinc. If the reaction rate is increased or is allowed to continue at lower temperatures during the cooling down period, a small percentage of iron (approx. 0.5% Fe) can be drawn from the steel to the surface of the coating. This results in the darker, more matte, or sometimes even a spider web like finishes.

It is common for an article to have adjacent areas of bright and dark colors, which will correspond to differences in the relative concentrations of the elements listed above and/or slightly different cooling rates. Basically, the steel in the darker areas has levels of certain elements that are out of range to produce a bright silver coating. You may notice brighter coatings around edges or bolt-holes, with a darker color in between where cooling was slower.

This effect is normal for higher reactive steels, and is not a detriment to the life-span of the coating. In fact, the darker areas, since they are indicative of higher reactive steels, often have a thicker coating than a brighter colored area. Thus, they will last longer. Thicker coatings can be more brittle than standard coatings, so extra care in handling and installation is advised.

Interestingly, everything that gets galvanized comes out bright shiny silver… at first. When items turn darker or matte gray, this happens while the part is suspended in the air, cooling. We certainly hope that everything stays bright and shiny; but every galvanizer, on occasion, has to helplessly watch freshly galvanized product turn dark in front of their eyes, just hanging there.

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