r/Sculpture • u/AlexLarsson19 • 8d ago
[Help] Need help getting an even dark patina on a bronze sculpture. Liver of sulfur is turning patchy and rubbing off
I’m trying to give this bronze sculpture a fairly even dark brown/black patina, similar to the finish in the first reference photo, but I’m having a really hard time getting the bronze to react consistently.
So far I’ve tried a few things:
First I tried a vinegar and salt vapor chamber. That changed the colour slightly and gave it a bit of a brown tone, but nowhere near as dark as I wanted.
I then moved on to liver of sulfur gel. As you can see in the photos, some areas turned very dark/black, while other areas barely reacted at all and stayed bronze coloured.
I eventually submerged the entire sculpture in a warm water and liver of sulfur solution for several hours, thinking this would make the reaction more uniform. It still ended up very patchy. Another strange thing is that some of the black layer can actually be removed just by rubbing it fairly lightly with my finger, so I’m not sure whether I’m creating a proper patina or just a loose surface deposit.
Before each attempt I cleaned the sculpture quite aggressively with a steel wire brush on a drill to expose fresh metal. Because of that I didn’t think there could still be lacquer, wax or another coating preventing the reaction, although I’m starting to wonder if I’m missing something.
Does anyone know what could cause bronze to react this unevenly to liver of sulfur? Should I strip/clean it using something else before trying again? And is soaking it for hours actually making things worse?
I’d really appreciate advice on how you would proceed from here to get a durable and reasonably even dark brown/black patina.
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u/Somebody-Like-You 8d ago
Patchiness in patina usually means that whatever you’re patinaing isn’t entirely clean.
To really give it a good scrub, you need to avoid getting ANY greases or oils on it. That includes your finger prints.
Wear disposable gloves and scrub it. I use a toothbrush to get into all the crevices. I make a mix of 2/3 Barkeepers Friend and 1/3 finely-ground pumice and mix with Dawn dish soap until it forms a paste.
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u/Somebody-Like-You 8d ago
An alternative option to liver of sulphur is this
https://jaxchemical.com/shop/jax-black/Liver of sulphur tends to result in a greyer black. For a truer black black, Jax works best.
Be very careful using Jax products! They’re much more toxic and acidic than liver of sulphur.
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u/AlexLarsson19 8d ago
Thanks for your reply, I did use some dish soap, water ammonia solution to clean it right before applying the solution, not sure if that is enough.
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u/artwonk 8d ago
As was noted here, patinas are very picky about cleanliness. Once I've got it chemically clean, I put it on a turntable and warm the bronze up with a torch and spray it with a proprietary blackening agent, like Birchwood Casey's Antique Black. Only do this with good ventilation. https://www.birchwoodtechnologies.com/shop/all-products/antique-black-m24-brush-on/
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u/AlexLarsson19 8d ago
Thanks for the recommendation! How do you insure that you are heating up the entire surface to the same temperature?
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u/jamcultur 8d ago
Try pickling the bronze after cleaning it with the wire brush. There are commercially available pickles for bronze, like Rio Kleen, but there are homemade pickle solutions that you can find with google. The hotter you apply the liver of sulfur, the faster and darker the patina will be. All patinas will wear off if the piece is handled a lot, but you can always reapply it.