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Iron

We work with local blacksmiths and iron designers to clean new works of art in iron

Ironwork that has been allowed to become seriously corroded tends to expand and appears laminated. While much of this will be removed by blasting it has weakened the original metal as the surface has corroded away.  The laminations can form under great pressure where two metal elements and fixed or welded together, then corrode over time, and the lamination become as hard as steel.  Sometimes these areas cannot be entirely removed because they are so hard and under pressure, and will always be the first areas to deteriorate as the corrosion continues to consume the base metal over a period of time. (Link  Picture laminated metalwork in About corrosive salts)

Wrought iron gates and the like can be cleaned and protected by Hot Metal Flame spraying, to resist further corrosion. Zinc wire is melted in an oxy-acetylene flame and sprayed onto the blasted metal surface. This is rather like a portable version of galvanising, which is done by dipping items in molten zinc. The zinc surface must be primed with an acid etch primer to ensure good adhesion of subsequent paint finishes. (Link to Flame spraying hot metal)

About Corrosive Salts
Wrought iron and cast iron are course grainy metals and comparatively porous structures which allow moisture and corrosive salts to get deeper into the surface of the metal than with say steel. When blasting them, they blast clean and look great - for a while - but the surface soon starts to oxidise (rust). This is because invisible salts are in the surface of the metal where the blasting can’t reach them.  We take the item outside and hose it down with water and the rust forms almost before your eyes, then we blast it again, and until. we are happy the salts are gone. Our phosphate treatment helps to stabilise and protect the surface until it is painted.   (Link rusty lamp post after washing between blasts).