12. Dial Finishing - Bronze Dial

To make a dial with an interesting finish, I decided to use the chemical patina process instead of paint to give the dial color. The interesting thing about a patina finish is that is it not completely uniform and has a lot of character and depth which can be seen in the subtle changes in the dark brown tone of the finished dial shown below:

Process for applying the patina

Preparing the machined bronze part:

From my experiments I found that to get an even, consistent patina, the substrate needs careful preparation. The two main attributes that affect the uniformity of the patina are the surface roughness and presence of oils or contaminants on the surface.

To make the surface roughness consistent, I sanded the dial with progressively finer sandpaper ending with a final sanding at 3000 grit. Having a surface that is too smooth does not give the patina chemicals surface area to react uniformly. Also, sanding and cleaning just before applying the patina makes the surface most reactive since it has not had time to naturally oxidize.

To make the surface clean, I first washed off the part after sanding with distilled water and a toothbrush. I then cleaned it with Sculpt Nouveau’s metal degreaser and then washed the part again with distilled water. I then pat-dried the part with a lint-free paper wipe. I actually had to re-do the patina multiple times, cleaning and stripping off the previous patina because either some debris fell on the part or the patina was not uniform enough. The picture below is the part prepped for my final attempt. That is why the outside already has a patina coating on it.

Applying the Patina

For this dial, I used Sculpt Nouveau’s Antiquing Patina which turns bronze very dark brown. I chose this because my original through was to make the dial black with the contrasting gold chapter ring, but after playing with patinas, I wanted to preserve some of the warmth of the bronze. The antiquing patina achieves that because although it makes the part very dark, you can still see the warmth of the bronze coming through.

The patina solution was sprayed over the part and you can see it starting to change the color of the bronze in the picture below.

You can see the how dark it gets in just a couple of minutes from the next picture.

Once the color developed to the shade I wanted, I cleaned the part with distilled water to neutralize the patina reaction and wipe off the residue created by the reaction. The end result is an almost black looking part with a matte finish, shown in the next image.

Chapter Ring and Sealing the part

The part was designed so the chapter ring is around 0.015” higher than the rest of the dial. This was done so I could sand off the patina on the chapter ring after the patina process to reveal the gold-bronze color and have it contrast with the rest of the dial. So, after my final patina application, I carefully sanded the patina off the chapter ring, shown in the next image.

To seal off the bronze from rust and oxidization, I sprayed on 2 coats of Sculpt Nouveau’s Clear Guard. This made the dial glossy. I was originally pleased with the glossiness, but I find that I don’t like it as much now because it makes it harder to read time because the glossy dial makes the crystal (top glass) more reflective. If I do this again, I will use a matte clear coat or texture the part more before applying the patina.