Rosenberg - Oxidation or "Rust Never Sleeps..."
Fabrication is complete on the Rosenberg's "modern" planter box. Today's task was to instigate oxidation on the exposed faces of the structure. I had a little guidance from Rick Lopez (and Paul!) at Iowa State University's IPRT Company Assistance – Materials Group. I did a little investigation on my own on the internet with little satisfaction prior to speaking with them. At a past employer, I had seen this process done in a day with consistent results, but didn't know the chemicals used. Muriatic acid was suggested by Rick to remove the mill scale on the hot rolled steel...and it worked beautifully.
I didn't have the time to apply numerous applications of a highly diluted acid over a week's time. Thus, the sculpture was taken outside and given a splash in the water before having some acid poured upon it into the areas where water had pooled while it was lying horizontally. The acid reacted instantly with the mill scale dissolving quite quickly. I used a disposable, bristled paintbrush to spread the diluted acid to the areas that had yet to react chemically. Places where the scale didn't immediately dissolve were given 5-10 minutes to soak. When the scale became difficult to remove with dirtied acid/water mixture, the entire surface was rinsed with fresh water. The smaller of the two areas (third and fifth photos above) required two applications. The larger area (first and fourth photos above) was unable to lay flat and had to be leaned at an angle, thus requiring four to five rounds of etching. After the mill scale was removed and the surface was a white/silvery sheen, it was rinsed with water one more time. A final misting of the acid/water mixture was applied and then allowed to dry. The mixture ratio of the mist was approximately 5:1 - 5 parts water to 1 part muriatic acid. Always add acid to water, never water to acid.
Before performing this, I took every precaution to protect myself and my surroundings. Safety glasses, chemical-resistant rubber gloves, leather boots and a respirator were all used during this process. Additionally, I did this outside in an spacious, open area, free of any obstructions. I personally would NOT recommend performing this inside unless you have the proper ventilation...i.e., a box-fan is NOT proper ventilation.
Hopefully this helps others looking for a quick rust "patina" when dealing with mild steel. All the supplies and safety equipment were purchased at Lowe's.