I randomly got given the opportunity to work on a pretty unusual project. An artist called Andrew "Stoneface" Vickers started a project to replicate his sculptures as small bronzes. He typically makes stone carvings cut into natural boulders, rock faces, etc. In order to replicate them as smaller pieces, the local university has been taking digital scans through some kind of technical wizardry to make computer models of his work which could be 3D printed. An art foundry did the castings, but their patina job wasn't up to scratch. My name got dropped at the local gallery as someone who knows about these things, so I was commissioned to provide the finish. I've just got done with the prototypes and I thought I'd share the recipe and technique I used. The idea was to create something natural which wouldn't look out of place when mounted on a rock base. I went to see the originals and they were located in a forest by a stream. Moss and lichen had grown over them in random patterns, so I knew I had to replicate that effect. I started by putting the pieces through a sandblaster to give me a clean canvas. The foundry who had cast the pieces had cast directly from the 3D print and the crevices and indents looked pretty rough and spongy, so I felt I had to disguise the defects with something dark. So I made up a strong liver of sulphur solution dip and let the bronzes corrode until they were completely black and the patina could be rubbed off like soot. I took a Dremel with an abrasion wheel and brushed off the patina, returning the exposed sections back to base and leaving the crevices black. I then gave them another sulphur dip to turn the exposed sections a coppery colour which completed the base coat. On to the torch. I mixed up some ferric nitrate solution (2 teaspoons in 1/4 pint) and some cupric nitrate solution (3 teaspoons in 1/4 pint), and then I pored a 50/50 mix of each solution into a separate container. I applied the ferric to all off the coppery sections with a brush, trying to avoid the black as much as I could and mixing it up with the 50/50 whenever I felt the colour was getting too dark or to add highlights to specific areas. Next I applied the cupric with a brush, trying to build it up evenly with a slight bias towards the crevices to tie everything together. I tried my best to avoid blocking the colour while representing it everywhere ununiformly. Controlled chaos you could say. Last step was to give it a light spray with enamel varnish to seal it. The picture doesn't quite give it justice, but the end result is a chocolate brown and black, with green and occasional red streak of marbling.
