A bronze equestrian statue King Charles IV of Spain that stands in Mexico City’s Plaza Manuel Tolsá has been damaged beyond repair by a botched and unauthorized “restoration” ordered by city officials. Cast in 1802 by artist and architect Manuel Tolsá (after whom the plaza is named), the statue is legally designated a historic property and is therefore under the purview of the National Institute of Anthropology and History (INAH). By law, any work on the piece must be authorized by INAH but in this case the Historic Center officials didn’t even apply for a permit until after the restoration was already in disastrous progress.
The city contracted one Arturo Javier Marina Othón of Marina Monument Restoration to clean, restore and maintain the bronze and its pedestal. He stated up front that he would only apply a weak 30% solution of nitric acid to clean the surface dirt and pollution, but when INAH experts examined the statue to report on the damage, they found a can of partially used 60% nitric acid on the scaffolding. Nitric acid in that high a concentration just eats through metal. Neither nitric nor any other inorganic acid have been used in restoring metals since the 1950s when conservators finally realized how much damage they cause.
Othón denies having used 60% nitric acid. He insists he only used 30% and that it’s a perfectly cromulent material for cleaning the outer grime layer of a bronze statue. In his opinion, he is being scapegoated to distract the public from the city’s failures to protect its cultural patrimony which could certainly be an element, but at the same time, there’s no denying the fact that the acid very obviously went far deeper than the top grime layer to expose the soft coppery underbelly of the statue.
Analysis of the statue’s dark, almost black patina done in September before the so-called restoration found that it was composed of oxide, carbonates, sulfur and sulfates under a layer of grime. Those compounds are what is known as passive corrosives, meaning they’re stable byproducts of exposure to environmental elements like oxygen, rain, carbon dioxide, sulfur compounds. They don’t damage the metal but rather form layers of protective coating.
Only 35% of the sculpture was directed treated with strong nitric acid, but 50% of it has been damaged by the acid dripping down from the application site. As a result, half of the patina is gone forever and the newly exposed bronze is particularly susceptible to corrosion. The strong acid also dissolved the less stable elements of the bronze creating an alchemical alteration of the material itself. Bronze alloy is made of copper, tin, zinc and lead. The nitric acid attacked the tin and zinc dissolving them and leaving behind shiny pink copper. The acid also pitted the surface, vastly increasing the area susceptible to corrosion. They used metal brushes attached to power tools to polish the metal, which of course did a whole other irreparable number on the bronze. There are patches of melted statue staining the stone pedestal now, runoff from the horse and king’s suppurating acid wounds.
The litany of incompetence doesn’t end there. The site was dirty, with trash and unused iron bars from the scaffolding scattered around. The iron stained the marble base and wooden planks trapped moisture in the area to compound corrosion problems. The scaffolding itself was apparently erected by drunken toddlers who had the brilliant idea of stabilizing the structure by tying a few bars to three of the horse’s legs, one of which already has a large crack in it. Some scaffolding planks were supported by the rump of the horse which puts it in danger of friction damage and further corrosion. It’s amazing the whole crew didn’t wind up in a pile of broken arms and legs.
INAH’s report strongly urges immediate intervention to stabilize the statue and restore it where possible. All conservation plans will be submitted to INAH for prior approval, needless to say, and you can bet they’ll be extra vigilant.
EDIT: I originally wrongly attributed the restoration order to the Historic Center Rescue Trust, a private organization founded by multi-billionaire Carlos Slim that has dedicated millions of pesos and much hard work to the revitalization of Mexico City’s historic center. This was my own erroneous reading of the original Spanish. In fact the restoration order came from city officials. I’ve removed the paragraph where I discussed the Trust and have redirected all references to the real culprit.
I apologize for the mistake. Many thanks to the anonymous commenter who corrected me.