Why Coat Bronze
The use of wax to coat bronze sculpture has a long tradition.
Archaeological evidence of the 'hot-wax' technique for creating bronze jewelry dates back as far as the first evidence of bronze itself - around 3500 BC. So I imagine that it wasn't too long before someone noticed how nice a bronze statue or pendant looks when polished with wax, and how it protects against fingerprints and weather.
This is my theory, but regardless of how it started, the use of wax to coat metal sculpture, particularly bronze, started long ago and is still going strong today.
The Trouble With Wax
I've used wax myself on sculptures. But recent research definitively shows that new products are better. After using a particular polymer known as Everbrite, I'm totally convinced that polymers are better in so many ways. I chose Everbrite because it has a track record of over 30 years - the longer something's been used successfully, the more I trust it.
The Advantage of Polymer
First, let's talk about application. Polymers are much easier to apply. Simply paint it on. Anyone can do it. Whereas wax has to be applied hot requiring an experienced conservator. Additionally, before applying wax, the old has to be removed and the surface cleaned. With Everbrite, yes, any wax, grease, and dirt needs to be removed, but if you're re-coating over a polymer, no removal is necessary.
Sure, a polymer coating needs to be cleaned, but that's a much easier process of wiping with water and cloth. Furthermore, when you apply a polymer over a polymer it 'self-anneals', meaning, it bonds to the old coat automatically. Huge plus over wax! By the way, unlike most paints, polymers also 'self-level', meaning that they do not streak when applied at the right temperature.
Now let's look at another benefit of polymer, protection. Only in the last couple of decades have we developed the technology to determine just how ineffective wax is. Research conclusively shows that even the best quality wax doesn't last as long as we thought and polymers last much longer.
How long wax lasts on a sculpture is purely a guess. Some conservators claim up to two years. Others say three months. The truth is, no one really knows. For outdoor sculpture, it all depends on the weather. It's so variable that wax on one side of a sculpture may weather more than the other side. To know just how long wax lasts, you need to test the particular sculpture which is a time-consuming and expensive process. I'm shaking my head, because why even do this when we know that polymer lasts longer, up to ten years!
And it's removable with solvent. Polymer coatings will darken verdigris, and one of my client's did not like this, so I easily removed the polymer coating with xylene.
Everbrite also provides UV and anti-oxidant protection, and does not yellow. Frankly, I think it's simply nonsense to ever use wax again on outdoor sculpture.
Assessing Different Acrylic Polymers
I rely on the US Park Service and the Getty Conservation Institute for the latest research on best products and practices. Unfortunately they have not yet studied any acrylic polymers other than Incralac which they found superior to wax.
Acrylic polymers were first developed in the 60's. Incralac was the first and still widely used today. Improved acrylic coatings followed with Permalac and Everbrite about 30 years ago.
Incralac and Permalac both last outdoors 3-5 years. Incralac is known to peel so it must be removed before re-coating. Everbrite lasts 5-10 years and along with Permalac does not need to be removed to re-coat.
All provide UV protection, self-anneal, and self-level.
Everbrite provides any gradation of satin or matte finish desired at no extra charge. Permalac now comes in a satin finish but no gradations are yet available. Incralac is coated in wax to achieve a satin or matte finish.
Four coats of Permalac are required for outdoor sculpture. Everbrite just 2. So for cost, protection, and ease of application I prefer Everbrite.
One criticism of polymer is that it's too shiny or just doesn't produce the same look as wax. This was true for early versions, but not any more. Manufacturers now mix any shade of satin or mat finish desired. In fact, the sculpture presented here is an example of just such a test of many different shades before the artist and I found the perfect match. The Everbrite company mixes any shade requested at no extra charge.
One drawback is that any polymer is solvent-based so it's flammable, and can irritate skin, eyes, and lungs. Thus, gloves, respirator, and eye protection must be used. Certain plastic containers and brush bristles will melt on contact with solvents, so I use metal containers and natural-hair brushes, available and inexpensive at any hardware store.
The final comparison is expense. When you think about all the issues mentioned above, polymer is hands-down less expensive than wax.
Coating 'Whale Dance'
I most enjoy installing and restoring sculpture when I work with the artist.
This job was just that. I met the sculptor Jim Sardonis last year when he asked me to remove graffiti from one of his sculptures. Now he wanted me to clean and coat this wonderful sculpture.
The first step was a close inspection and estimate of what the job requires. That done, I asked the artist if he had a preferred product for coating his sculpture. This is a touchy question because Jim no longer owns this sculpture. It was purchased for permanent public display. Thus, Jim doesn't really have any say in this, though recent laws give artists some control over their art even after they sell it. Nonetheless, any decent conservator wants to know and respect an artist's wishes when reasonable. And like most sculptors, Jim preferred wax, but after I presented the wax versus polymer issue, Jim decided to try a polymer.
Polymer is particularly protective in the harsh freeze-thaw weather cycles we have here in Vermont and throughout New England. Acid rain, bird droppings, and pine needles add an extra degree of stress on the surface of metal sculpture. Wax lasts only months in these conditions. Polymer last years.
Next we worked on a perfect shade of satin. We painted many small patches right on the sculpture. These could be easily removed later. Everbrite sent us several small test batches. Jim made the final selection. We stayed six feet apart throughout to adhere to our state's Covid-19 precautions. The final selection turned out to be 1/4 of the usual satin chemical mixture. We also tested brush versus wipe. The coating takes only 20 minutes to dry to the touch and 60 minutes between coats. I called Everbrite and they mixed and shipped our custom request within a day.
I cleaned the sculpture surface of all the old wax and accumulated dirt using mild soap and water. For problem areas such as a few spots of mild corrosion, I used a solvent which does not harm the patina.
I applied two coats of the custom-mixed Everbrite satin that Jim chose. The first coat sealed small cracks and pits.
More and more conservators now use polymer coatings. This is the best recommendation of all since the conservation industry is quite careful. Conservators are not known for using products such as polymers that are 'only' 30 years in use!
This particular coating restored a new look identical to the original dark brown bronze patina.
No maintenance is required other than wiping with a cotton cloth and tap water. When the coating fades, just reapply a new one without removing the old. Anyone with painting experience can do it.
Two coats will last up to ten years depending on weather conditions. Polymers are so durable that I offer a five-year warranty to all my clients.
1. Latest European study on wax, 2002, https://www.researchgate.net/publication/303158807_Protect_our_European_outdoor_bronze_monuments_Good_Practice_Guide_Culture_2000
2. Assessing the Protective Quality of Wax Coatings on Bronze Sculptures Using Hydrogel Patches in Impedance Measurements, 2016, Downloadable PDF at www.mdpi.com P. 10 - polymers are more protective than all waxes tested.
3. Latest research abstracts on polymer coatings for bronze, 2020 https://www.researchgate.net/publication/222801665_Developing_and_testing_a_new_generation_of_protective_coatings_for_outdoor_bronze_sculpture
4. More research, 2019, https://www.sciencedirect.com/science/article/pii/S0300944018309743
5. Latest GCI Research: https://www.getty.edu/conservation/
6. Anecdotal comparison of Everbrite and Incralac: https://www.everbritecoatings.com/public-art
7. Latest CGI bronze restoration: http://blogs.getty.edu/iris/revitalizing-barbara-hepworths-figure-for-landscape/
8. Latest National Park Service research: https://ncptt.nps.gov/blog/ndsu-outdoor-bronze/
9. Latest Getty Research: Incralac vs Permalac: chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/viewer.html?pdfurl=https%3A%2F%2Fwww.getty.edu%2Fmuseum%2Fconservation%2Fdecorativearts_and_sculpture%2Fimages%2Fdasc_featuredproject_sculpture.pdf&clen=596502