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Toning Metal Leaf with Liver of Sulfur
Exposed to the elements, many metals oxidize. When they do, they change colors. Copper and bronze will sometimes develop an attractive verdigris of green. As they weather, metals will also darken, turning their brassy colors to antique hues of brown. The term most frequently used for the weatherworn coloration that metals develop is patina.
With the application of a little chemistry, you can replicate the effect in a few simple steps without having to wait for Mother Nature to do her thing. There are many different recipes for creating a patina on a gilded surface. In fact, voluminous books have been published on the subject. The Society of Gilders journal, The Gilder’s Tip, will also occasionally have articles on chemical patination. Many of the chemical formulations are toxic or hazardous to your health. When working with chemicals, it is prudent to follow some basic safety precautions:
- · Always read and heed the safety instructions pertaining to the product that you are using.
- · Many chemical formulation produce harmful or toxic gases. Always work in a well-ventilated area.
- · Always wear chemical gloves.
- · Keep as much of your skin covered.
- · Always wear safety glasses.
A relatively safe chemical to use to create a patina is liver of sulfur. Below are before and after pictures of a gilded carving treated with the chemical.
My carving of grapes was first gilded with Dutch metal leaf.
After treatment with liver of sulfur, the metal leaf darkened and developed some interesting hues.
Liver of sulfur is available in a few different forms: dry chunks, premixed solution and a gel. The drawback of the dry chunks is that it has a shelf life. In solid form, liver of sulfur can rapidly degrade and lose its potency when it is exposed to oxygen.
You can use liver of sulfur for patination of surfaces which have been gilded with metal leaf, such as Dutch metal leaf, copper leaf and silver leaf.
NOTE: Pure gold does not oxidize and does not tarnish. If gold darkens, it is often caused by oils deposited on the surface, which act as an adherent for dirt. That’s why you should keep your grubby mitts off of the real thing.
Skin oils and grease can also cause unwanted effects, such as fingerprints, when you are chemically treating gilding. The reason is that oils will act as a resist preventing the chemical from reacting with the surface of the metal leaf.
To remove any contamination from the gilded surface, you must clean it, washing the article with a mixture of dishwashing detergent, a couple of tablespoons of ammonia and warm water. So that you don’t re-contaminate the surface wear latex gloves while you are working. Rinse the cleaned piece with clean water.
The next step is to dip the piece in a container with the patina solution. To create the patina solution, mix a tablespoon of liver of sulfur in a container of warm to steaming hot water. To this mixture, you can pour in a tablespoon of ammonia and mix the solution. The addition of the ammonia will promote the creation of unique and dramatic coloration. The container should be large enough to accommodate the gilded article.
While this patina solution will work if the water is cold, it works better in warmer water. The reason is simple. Chemical reactions typically accelerate at higher temperatures.
HAZARD: DO NOT use boiling water in the patina bath. Boiling water will create sulfur dioxide gas, a corrosive, which is hazardous to breathe. Low level exposure to sulfur dioxide can cause irritation to your eyes, lungs and nose. High level exposure can cause permanent eye damage, breathing problems and burns to your skin. Make sure that you work in an area with good ventilation and air flow.
As the article is in the patina bath, carefully watch the change of color on the surface of the metal leaf. When the color darkens to the desired degree, take the piece out of the water. After removal from the bath, the color will continue to darken.
To stop the oxidation from proceeding, you must dunk the piece in a neutralizing bath of baking soda and water. Leave the article in the solution for a few minutes. In mixing this neutralizing bath, add ¼ of a cup of baking soda to every 32 oz. of water. Stir the solution until the baking soda has dissolved thoroughly.
After the gilded article has been darkened, you can clean off some of the patina to create a two toned effect which accentuate the contrast between highlight and shadow. This finishing touch can enhance the dramatic presentation of the article.
Using a paste of baking soda, which is a mild abrasive, and a little water, you can gently clean the patina from the high spots of a carved piece or a textured surface. This can create a dramatic contrast between highlight and shadow. A piece of cotton is useful in polishing the gilded surface to the desired effect. After treating the piece with liver of sulfur, you can protect the surface with a clear coat, such as Frog Juice.