Use clean containers to hold the chemical solutions and don't use the same brush with different chemicals.
There are literally thousands of patina recipes. Make sure your object that you're applying a patina to is free of dirt and grease. You can scrub it with a solvent xylene or acetone works well for removing grease , or a bit of soap and water. Rinse it well with clean water and you're ready to go. Heat the bronze evenly. All steps are important but nothing can ruin a patina faster than having hot spots. Heat the entire piece to a straw yellow or honey gold color and then let it cool a bit.
Bronze is a good conductor and the heat will dissipate quickly to eliminate hot areas. The metal should be hot enough so water sizzles but does not ball up and run off sort of like when you used to spit on a clothes iron when you were a kid. You can test the temperature by brushing or spraying a little clean water on the surface. Bismuth nitrate is applied first with a spray bottle to give an opaque white coat.
Keep in mind that many layers of chemicals will be applied so build up the bismuth just enough so that the bronze is covered but no more.
- Hot Patina on Bronze.
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If the bismuth gets too thick, the chemicals applied on top of it will tend to flake off because it is not able to create a chemical bond to the bronze. After the undercoat is applied, begin to brush on ferric nitrate. Keep the piece warm by periodically applying heat with your torch. For this piece, the first layer of ferric nitrate was stippled on to create a modeled effect. If the sculpture is textured and you want to take advantage of it, don't worry about making the patina too even. Continue heating and applying ferric nitrate to the entire piece.
When stippling, be sure to rotate your brush so that patterns don't become evident.
Step 1: Clean Bronze Casting
After you're done with the ferric nitrate, begin applying cupric nitrate to add complexity. This layer is less even than previous steps to accentuate certain parts of the piece. You can focus more heat on certain areas to achieve darker tones or even put the torch flame directly on the cupric just after it's applied. This will make the cupric go opaque bluish-green. If working cool, be careful that you don't "drag" the chemicals underneath as this will lead to a muddy looking patina. Some of this layer can be done by dry brushing.
The Bronze Patina Book by Hugh Cornelius
Shake most of the chemical off the brush and very light brush the high layers of the piece. This is especially effective in bringing out the texture of a piece. Continue working the entire piece. Vary the amount and type of chemical to bring up the texture and add dynamism to the sculpture. Don't try to make it perfect or you will drive yourself crazy.
Keep in mind that you'll be applying a couple coats of wax at the end which tends to even out the piece and add surface depth. Darker patinas can be waxed when the piece is warm to add richness, while opaque patinas like the one in this instructable are better off being waxed when the piece has cooled. After the piece has cooled to room temperature, apply two coats of carnuba based wax. Stipple the wax over the entire piece, let it set for a couple of minutes, and rub it off with a clean, soft cloth micro fiber works well for this.
Apply a thin second coat and buff it out to give it a little sheen.
Susan Honiker, those are excellent tips and I agree that the book itself is excellent. What other types of sculpture do you do? Thank you. I am interested in Susan Honiker's comment on using shoe polish on bronze jewellery. Did the shoe polish colour last? I am thinking of using black Kiwi on a bronze bangle and finishing it with a sealant. Would appreciate your advice.
Thank you, Mairi. My husband and I are restoring a bungalow. The door hardware knobs and hinges are copper that mostly have tarnished over the years to a wonderful dark brown, looking a lot like the oil rubbed bronze finish that is so popular today. There are a few knobs and hinges that have been painted and I want to strip them and find a method of rapid aging them to match the dark finish on the majority.
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Any help would be most appreciated. I have a bronze piece that I cast silica bronze. I had to braze a few of my cast pieces together and though the brazing rod SAID it was bronze it is a much more brassy color AND does not take patinas like Liver of Sulfur or anything the same as the cast bronze!