The shiny surface of galvanised metal is often undesired by consumers and the general public. Manufacturers sometimes receive complaints regarding the reflectivity of certain products alongside requests to dull the shiny, galvanised finish. These complaints are often associated with galvanised products intended for outdoor use along roadways and among wildlife habitats. A dulled or weathered finish is often preferred to avoid safety issues for motorists and unnecessary or unpleasant disturbances in nature. The desired dull finish can be achieved using the following steps.
Allow the galvanised metal to age naturally if the product is not needed for installation immediately. Exposure to rain, dust and debris will allow the material to lose its reflectivity over time. Some galvanised metal products will show a significant decrease in reflectivity in as little as three days; however, for optimal results, the products should be exposed to natural weather conditions for a minimum of six months. Galvanised metal products that are not coated will become less reflective quicker than those with a protective coating or film.
Treat the galvanised metal with a solution of 1.4 kg (3 pounds) of copper sulphate crystals dissolved in 4.5 litres (one gallon) of water. Once mixed, add 285 ml (1/2 pt) of concentrated hydrochloric acid. Carefully spray on solution and immediately rinse with clean water. This technique should be conducted in a controlled environment so as not to allow hazardous run-off of chemicals.
Dip the galvanised metal into a 1 per cent nitric acid solution for 90 seconds if spraying the piece is not feasible. Rinse thoroughly after removing the metal. This method should only be used if the product contains only galvanised metal. The solution may damage other materials if the galvanised piece is attached to any other surface.
Apply a coat of primer to the galvanised surface to reduce the reflectivity of the new metal if no other option is available. Different primers are available that will dull or darken the surface to varying degrees.