Patinas for Your Jewelry
May 27, 2010 § 3 Comments
Thank you Shaiha, for your question. You got me thinking, and reaching for other resources. (http://shaihasramblings.blogspot.com) . Shaiha asked about a patina for brass. There are a lot of ways to color metals, depending on what color you are looking for. Many of the chemicals are hazardous; in fact, most are required to be shipped ground. I do mention a less toxic means of adding a patina to bronze. There is also a website listed that has a few handfuls of recipes for patinas, and a great book that’s on my wish list.
Patina. A patina is oxidation, a chemical change that occurs when metals come into contact with oxygen. Oxidation often happens naturally, and in those cases we aren’t often glad to see it. Oxidation can also be used as a decorative element in art and jewelry.
There are three forms of oxidation: hot, cold, buried. I have seen just hot and cold listed, with ‘buried’ listed under cold applications.
Cold patinas include patinas resulting from burial of the object, cold chemical patinas, and patinas created with fumes. These don’t need heat to produce change, but heat will destroy them.
example: for a vivid teal green:
- Ammonia or uric acid (if desired)
- sawdust, cat litter (used cat litter is better)
- Moisten sawdust or litter with vinegar (well moistened). Add ammonia or uric acid if you wish. Put the mixture in a bag with the bronze piece. Check on the piece after several days. The teal green happens with just vinegar. Bluer colors emerge if you add the ammonia.
The above method is one of the least toxic. It takes the longest, and you have very little control over the process.
Other cold processes, which happen at approximately room temperature, include gun blueing and liver of sulphur. These processes do happen more quickly if the piece you are oxidizing is hot. The chemicals involved are either stronger or more concentrated, to be able to work without heat.
Hot oxidation isn’t always considered a chemical reaction. Heat means the oxidation happens more quickly. It also means that heat is likely to darken it. The amount of heat, the chemicals involved, and method of application all affect how the oxidation appears. These involve the least time, are the most controlled, and don’t require quite as strong or harsh chemicals. That said, you need to know that if you are using heat, it is that much more dangerous.
Once the piece reaches the desired color, the oxidation needs to be protected. If not protected with some sort of coating, the piece may continue to discolor, or it may be easily removed. There are a number of things you can use as coatings, including renaissance wax.
There are great books on the subject. Here is one to look into:
The Coloring, Bronzing and Patination of Metals, by Richard Hughes, Michael Rowe
An interesting site and a variety of recipes that I haven’t checked out. Feel free to check it out.
**Standard disclaimer: I don’t recommend using any chemicals without proper training, equipment and experience. Any and all of these examples should be done with proper equipment, including (as examples) a fan hood that is directly above your work; a mask (respirator version); whatever else your instructors, lab assistants, etc. recommend.