Etching with acid

 

 

!!CAUTION!!

The fumes are very toxic!! Always use outside, with good ventalation. Make sure water is handy to dilute any spills.

The acid is Muriatic Acid, found at most hardware stores. I built a small fixture of Masonite and wood, which allows a piece of sheet metal to stand almost vertical. There is a gap in the bottom lip to allow the acid to drain off. The fixture rests on top of a plastic container, which is the resevoir for the acid. A second plastic container hold rinse water. I use two sizes of brushes, 1/2" and 1/8" wide. A simple pair of wood tweezers finish off the tools.

 

!!CAUTION!! 

Muriatic Acid will burn holes in clothing and skin. Use care when pouring and brushing acid.

Galvanized metal is coated with a zinc layer which protects the steel from rusting. Over time, the zinc is erroded, and the steel rusts. Here we use acid to etch away the coating in specific areas. Look at older sheet metal and study the patterns that develope. For this project, I wanted roofing that is just starting to rust, so I streaked some areas, and left the rest un touched. Notice how the acid bubbles up as it attacks the zinc coating.

   The surface of the sheet metal will change colors reflecting the degree to which the zinc is etched away. The areas where the steel is completely bare will be shiny. These are the spots that will begin to rust right away. The more lightly etched areas will rust over time.
   Use the wooden tweezers to move the sheet metal to the water bath to rinse the acid and stop the etching process.
   Leave the sheets in the water as you etch the rest of the pieces.
   When all the pieces are etched, remove them from the water bath and spread them out to dry. Occasionally spray them with water to start the rusting process. Notice that rust is just starting on the upper piece.
   This is a view of the finished installed roof on the freight house. The rusted areas are developing deeper brown colors, and will continue to change with time.
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