# What causes the blotchy pattern on galvanised steel?

**URL:** <https://boards.straightdope.com/t/what-causes-the-blotchy-pattern-on-galvanised-steel/662137>\
**Category:** Factual Questions\
**Created:** [June 28, 2013, 4:34pm UTC](https://boards.straightdope.com/t/what-causes-the-blotchy-pattern-on-galvanised-steel/662137 "2013-06-28T16:34:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\
**Post date:** [June 28, 2013, 4:34pm UTC](https://boards.straightdope.com/t/what-causes-the-blotchy-pattern-on-galvanised-steel/662137/1 "2013-06-28T16:34:27Z")

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Galvanised sheet steel typically bears a patina of irregularly-shaped (although quite uniformly sized) blotches, some dull grey, others brighter silver and every shade between.

What are these blotches? Are they flat crystals of zinc?

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**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\
**Post date:** [June 28, 2013, 4:45pm UTC](https://boards.straightdope.com/t/what-causes-the-blotchy-pattern-on-galvanised-steel/662137/2 "2013-06-28T16:45:04Z")

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The answer is yes, these are the individual zinc crystals.

The different shades result from the different (random) orientations of these crystals.