The cleaning of a colonial wall in Old San Juan has sparked controversy in Puerto Rico, since those who opposed it say it could destroy the structure's historical value.

The cleaning with a high-pressure washer machine made it lose its patina, a sheen of grayish-brown or green caused by oxidation, which forms on a number of materials as a result of dampness, according to several experts.

The city wall extends from the Port of San Juan to the headquarters of the Puerto Rico tourism agency in Paseo La Princesa street, above which is located La Fortaleza, the official residence and offices of the Puerto Rican governor.

Jesus Manuel Ortiz, press secretary of Gov. Alejandro Garcia Padilla, told El Nuevo Dia newspaper that the work of cleaning came as a result of concern about the safety of the centuries-old city wall.

"The issue of the wall came up because in an inspection we noticed all the vines and other vegetal material growing on it," he said.

The restoration plan consisted of blasting away all the vegetal material, dirt, mushrooms and bird droppings, in a project coordinated with the U.S. National Park Service.

Archaeologist Luis Chanlatte told El Nuevo Dia that the biggest mistake in the cleaning was the use of a high-pressure washer, since the stones of the 17th-century wall are held together by a sand and lime mixture that lacks the solidity and strength of cement, so that the water pressure could have removed part of the mixture with the consequent damage to the structure.

"If that high-pressure washer removed any of the mixture that joins the stones of the wall, the stones can come loose and begin to fall. There is that danger," he said. EFE