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.
And so the use of wax to coat metal sculpture, particularly bronze, became a tradition that 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 acrylic polymer known as Everbrite, I'm totally convinced that acrylics are better in so many ways.
The Advantage of Acrylic Polymer
First, let's talk about application. Acrylics are much easier to apply. Simply paint, spray, or wipe 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, previous wax needs to be removed and the surface cleaned just as carefully, but if you're re-coating over an acrylic, no removal is necessary.
Sure, an acrylic coating needs to be cleaned, but that's a much easier process of wiping with water and cloth. Furthermore, when you apply an acrylic over an acrylic it 'self-anneals' meaning, it bonds to the old coat automatically. Huge plus over wax! By the way, acrylics also 'self-level', meaning that they do not streak when applied at the right temperature.
Now let's look at another benefit of acrylic polymer: protection. Only in the last couple of decades have we developed the technology to determine just how effective wax is. Research conclusively shows that even the best quality wax doesn't last as long as we thought and acrylic 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, you can't be certain unless you test it. For outdoor sculpture, it all depends on the weather. It's so variable that wax on one side of a sculpture will 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 go to this effort and expense when we know that acrylic polymer lasts longer, up to ten years!
Everbrite also provides UV and anti-oxidant protection, fills pin holes and hairline cracks, and does not yellow.
Frankly, I think it's simply nonsense to ever use wax again on outdoor sculpture. Many of my sculpture conservation colleagues now agree - a recent poll shows that most conservators now use acrylic polymers 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 drawback is that acrylic 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-based products such as these, so I use metal containers and natural-hair brushes, available and inexpensive at any hardware store.
There is now a water-based Incralac, but it is not recommended for patina treated bronze which is most outdoor bronze sculpture.
Coating 'Whale Dance'
I most enjoy installing and restoring sculpture when I can work with the artist.
This job was just that. I met the sculptor Jim Sardonis when he asked me to remove graffiti from one of his sculptures. Now he wanted me to clean and coat this wonderful sculpture.
- Restoration of Maya Lin Sculptures in Istanbul
- Dusting the Buddha
- Sculpture Restoration in London
- Graffiti Removal in Vermont
- Bronze Conservation in Athens
- Unusual Pool Tile Art Restoration in Manila
- Bronze Conservation in Montpelier
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 acrylic issue, Jim changed his mind in favor of Everbrite.
Acrylic polymer is particularly protective in the harsh freeze-thaw weather cycles that we have here in Vermont and throughout New England. Acid rain, bird droppings, and pine needles add an extra degree of stress on outdoor sculpture. Wax lasts only months in these conditions. Acrylic polymers 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 carefully cleaned the 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 acrylic polymer coatings including the Getty Conservation Institute.
The Everbrite 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. Acrylic polymers are so durable that I offer a five-year warranty to all my clients.
1. Latest European study on wax: 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: www.mdpi.com P. 10 - polymers are more protective than all waxes tested.
3. Latest research abstracts on polymer coatings for bronze: https://www.researchgate.net/publication/222801665_Developing_and_testing_a_new_generation_of_protective_coatings_for_outdoor_bronze_sculpture
4. More research: 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/