[Borsheim Arts Studio]

Bronze Patina Process

by Kelly Borsheim

Copyright © 2004 Kelly Borsheim
All Rights Reserved

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receiving a patina
(bronze art)

After I have finished my original sculpture (usually in plastilina or wax), I spend a lot of time examining the piece prior to moldmaking. Each artwork is a unique composition, so each step of the lost wax bronze casting process requires forethought. My husband John is my moldmaker. He and I will discuss how best to make the mold (where to place seamlines, etc.), usually over several days. On complicated or large pieces, I will often call the foundry that will cast the bronze for a consultation. Each foundry works differently and I can get a better result if I include those technicians in the mold-making process.

After the bronze has been cast, it is then welded into one piece (as needed for large or thick works) and chased (resculpted in metal until it duplicates the original work). At this point, the bronze is ready for the finish or patina. To me, the patina is a bonus. As a sculptor, I want my work to speak in sculptural terms, meaning that the idea should be communicated prior to and independent of any patina that is added to the work. I like the idea that if 1,000 years from now, archeologists were to dig up my work (heaven forbid it get buried!) and the patina was gone, the work would still be complete in its execution and idea. However, the patina can enhance a 3-d work. So here we go . . .

The finished bronze is thoroughly (sand)blasted with tiny glass beads to remove any leftover investment mold and to clean finger oils that may have attached to the bronze during handling. There are many types of patinas, although they are usually broken down into two groups: hot and cold applications. I generally prefer the hot applications. This means that the bronze is heated with a torch before a chemical is applied to color the metal.

I have been exploring my aesthetic in the patina realm for many years now. And I am constantly intrigued by the more stone-like faux finishes, probably because I love stone so much. It also has to do with my preference for a non-shiny finish on human skin, although in the case of Shield I like this look. John, my moldmaker, is also my patina man. Although I sometimes have the foundry apply the patina while I oversee the process, more and more John and I work on these ourselves.

The sculpture that John is applying a patina to on this page is my garden-sized bronze Gemini, number 2 in the edition. The bronze sculpture is heated with a propane torch until the whole thing is consistently hot. This can be tricky since thicker areas of bronze take longer to heat and stay hot longer, while thinner areas tend to either overheat or cool down too quickly once the heat is removed. So this takes a bit of practice. The images here show the first chemical application.

There are different ways to apply these chemicals or chemical/pigment combinations - from brushing to spraying to rubbing and scrubbing. Each patineur uses what works for different effects, much in the same way a painter applies various strokes of paint to a canvas. There is much artistry involved in patina work and MANY variables. No two patinas turn out exactly the same.

[bronze art patina]

[bronze art patina] [metal patina]

[patina infrared thermometer]

John uses a handheld noncontact infrared thermometer, which uses optics to read the surface temperature of the hot bronze from a distance. I have never seen another patineur use such as tool, but John is a mechanical engineer and he loves working consistently using scientific techniques. He takes these readings throughout the patina process and reheats the metal as needed, being careful not to burn any previously applied chemicals.

[metal patina, noncontact thermometer]

[hot metal patina for bronze art]

[faux finish stone patina]

Here, you can see detail shots of the granite-like texture we are trying to achieve in this faux finish stone patina. Many layers of different, but complementary colors have been applied at this point. Below, you will see John applying a finishing layer to tie together all of the other applications of the patina. My job is to look for any missed spots or areas that I do not fully appreciate. This is difficult, especially on larger artworks because, like stone carving prior to polishing, the patina is rather paste-y looking and has a more consistent look than it will after the sealer has been applied. (The dappled light in our neck of the woods does not help either.)

[faux finish granite stone patina]

[faux finish granite stone patina] [faux finish stone patina] [faux finish stone patina]

Below are a few images of John applying thin coats of Incralac as a sealer to protect the patina and the bronze from the elements. Perhaps in the image on the left, you may see how the sealer darkens the patina and enriches the colors (the top of head has no sealer yet). Incralac, applied in many (around 6-8) thin coats is the industry standard for protecting outdoor bronzes. I spoke with the manufacturer, as well as my foundry about methods and mixtures of application, and tend to put a lot of trust in the art preservationists.

[bronze metal patina sealer, Incralac] [faux finish stone patina] [bronze metal patina sealer, Incralac]

Patina Aesthetics

Another point of interest: Patination is all a matter of taste. While some collectors and artists like to try to keep the patina as close to the original one as possible, others enjoy watching the patina change with age. Some even go so far as NOT to seal the bronze so that changes happen faster. You have probably seen many sculptures with various colored streaks (usually green) running down them from years exposure to rain or, in the case of fountains, chlorinated water. What you are witnessing is the erosion of the surface of the bronze. In other words, the sculpture is being damaged. But some people like this look. Private collectors may do what they like with their art. Public art, however, is another matter. And so the discussion continues . . .

If you would like to know more about bronze art preservation, I highly recommend the following books (click on the image to buy):

Cleaning and Caring for your Bronze Art

A sealer is intended to protect the sculpture from environmental elements, such as rain and bird droppings. It also will protect the art from oily skin as people enjoy sculpture via their sense of touch. For large and outdoor sculptures, I use the Incralac as a sealer. On smaller indoor artworks, I may use wax. If you buy one of my sculptures and are not sure of what I used to finish the artwork, please ask me. You will need this information to help you know best how to continue any maintenance you desire for your collection.

Please note that patinas are not indestructible. Sculptures, even bronze and stone, should be handled with care. Patinas may be scratched or discolored if something spills on them. It is wise not to lift or move a sculpture if you are wearing chunky jewelry or buttons on your shirt.

One problem with a hot patina is that if you do not like it, the only way to fix it is to do the entire process all over again - from sandblasting down to the bare metal to re-sealing. That said, a minor scratch may be touched up by applying colored waxes. Melting part of a crayon that is the right color gives you a soft wax to rub over the nick in the patina. But this really works best on patinas that have been sealed with wax.

Cleaning Your Bronze Sculpture:

For Incralac'd bronzes:
you may wipe the sculpture with a damp cloth or wash with Orvis soap - a gentle soap with no negative or positive charge that is great for removing oils and dirt. In Austin, Texas, I am told you may purchase that at Callahan's Feed Store. Orvis is a livestock/veterinarian soap, often used to clean goats. Quilt shops may also carry it, as it also may work well to clean fragile linens.

For waxed sculptures:
This sculpture may be cleaned by dusting lightly with a soft cloth or, if absolutely necessary, with a slightly damp (water only) cloth. DO NOT USE CLEANERS OR SOLVENTS or the wax finish will be removed. On occasion, you may want to maintain the beauty of the patina by adding a thin layer of Johnson's Paste Wax or Trewax and then lightly buffing the wax. If the sculpture is displayed outdoors, it is recommended that a new coat of wax be given the sculpture at least once a year.

I hope you enjoy your Borsheim sculpture for many years to come.

Thank you for reading!
Kelly Borsheim, sculptor

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Copyright © 2004 Kelly Borsheim
All Rights Reserved