I recently bought an antique bronze statue that had (in my opinion) spent some time in the ground. As a result, the statue was mineralised and covered with dirt. I removed the dirt easily with soap and water, but the mineralised patina remains. It isn’t crusty chunks of mineral, but more of an even layer of verdigris spread over everything. I know a bit about antiques and know that the general rule is not to mess with the patina as it is part of the value of the statue. But the patinas I have seen are usually a rich smooth brown and are very pretty. This verdigris isn’t and I feel detracts from the intrinsic beauty of the statue. So I am wondering if I might be able to recover the nice patina from beneath the verdigris. I don’t know what the bronze reacted with in the soil, but I would guess the usual oxides, sulfates, and carbonates are present.
Any antiquarians/metallurgists out there who can suggest some non-harmful cleaning techniques to remove the verdigris?
I work at a museum, and I have removed that green, bumpy covering from some of our artifacts. I warn you, to do it safely will take a looooong time, especially if the stuff is really rooted in there. Take a tiny piece of the batting and just sit there and rub. Just as a general guideline, it sometimes takes me about four hours to get an inch-square area cleaned when the verdigris is thick.
We use a product called Nevr-Dull. Most hardware stores carry it. It’s a soft cotton batting coated with a tarnish-cutting oil. You need to rub gently because even cotton wool can leave scratches on brass if you’re overly-enthusiastic. Make sure you pick out any cotton seed hulls you see in the batting.
Wear rubber gloves. The oil turns into a thin black mud when you’re using it and it’s almost impossible to get it out from under your fingernails.
After you’ve finished, the statue will be shiny and bright. We generally rinse using mineral spirits and a soft buffing cloth. Try to avoid leaving fingerprints on the finished surface because they make spots. (I wear cotton gloves during the final rinse-and-buff stage.)
The patina will return relatively quickly, especially if you’re in a humid environment. (I swore the other day when I saw that the headlights need another cleaning-- they’re starting to get that orange-brown shade after only a few months. That’s the beginning of patina.)
Another tip: when you get a can of Nevr-Dull, take out all of the contents and flip them over before stuffing them back into the can. The bottom pieces will have more of the oil on them and will make the job a little easier.
That said, if the statue is of real value, you might want to leave it as it is. I would have someone at your local museum examine it before I started cleaning.
Thanks for the good advice Lissa. I will have to go look for Nevr Dull.
I was wondering about the desired patina though. The way I see it, there was the original metal finish (dating several hundred years ago when the statue was cast). This would have ranged from coppery-brown to brassy yellow depending on the alloy. Then over decades to centuries, the statue would have developed a ‘nice’ patina - a rich, smooth lustrous brown to back. Then it was buried and became mineralised in the verdigris I was talking about. You mention that after the (looong) application of the Nevr Dull the bronze became ‘shiny and bright’. I assume this means it went back to the original finish?
I would want to avoid that. Assuming there is a nice patina hidden under the verdigris, is there a way to return it to that patina without going all the way back to the original finish?
Hmm, that makes sense. But given that the patina I would like to end up with took 100+ years to form in the first place, I think it is better for me to leave it the way it is. Thanks.
Of decades. Depending on the thickness of the piece, centuries.
A problem you may have if you decide to clean it off is if any areas got eaten up too thin. You’ll notice them when you’re cleaning, though, if they do exist.
You also may notice faint pockmarks on the surface of the metal once you’ve finished cleaning it.
The headlights on that car I mentioned were 100 years old and from the photos I’ve seen, I speculate they were covered in verdigris for about forty. After I finished cleaning it, you could see small pits where the coating had been particularly thick. You had to look hard to see them-- from a few feet away you’d never notice them.
From what I heard on Antiques road show you really should never clean old brass or bronze, just dust it lightly. If it is at all valuable then go talk to museums or local antique dealers for advise taking the piece with you if you can. They’ll tell you what you might do, and advise you on whether you should even attempt it with that particular piece.
I second the recommendation of having a professional take a look at it to make sure it’s not something of great value before proceeding. That’s always a good idea. That said:
The patina which adds value (both monetarily and aesthetically) is gone. It will return, but right now its condition is actually a drawback.
The vedigris is like rust and will eventually destroy the piece. Sometimes at my museum we take steps to neutralize it if we don’t want to clean it because it’s too fragile but nine times out of ten the first thing we would do if it was given to us is clean that gunk off.
Chances are, this is not a priceless piece. There were a lot of mass-produced bronze statues made in the Victorian times. (Classical styles were particularly popular.)