A floor mosaic of an anatomically detailed bull in one of Milan’s grand arcades is getting a sensitive makeover after being worn down by thousands of passersby honouring an unusual tradition.

Legend has it that grinding your heel on the bull’s testicles at the Galleria Vittorio Emanuele II guarantees you will return to the city.

“Because of constant pirouettes on the heel made by tourists visiting Milan, the pink tesserae that make up its testicles have been worn down, forming a small crater,” city authorities said.

The beige mosaic is part of the flooring in the 19th-century shopping arcade, near the Duomo cathedral. It represents Turin, which was then the capital of Italy.

Galli gets to work as tourists look on. Photograph: Stefano Rellandini/AFP/Getty Images

Gianluca Galli, a restorer, worked on the mosaic on Thursday as tourists milled around and looked at the windows of the first Prada store. “It’s probably a charming gesture, but also quite damaging for a work of art,” Galli said of the curious tradition.

He cut pieces of stone by hand after looking at designs from the period and taking an impression of the original bits. He said he would use epoxy resins instead of the original lime, and sand mortar to glue them down to better withstand tourists’ heels.

Unable to pirouette on the bull during the restoration, tourists performed a similar act on a neighbouring she-wolf mosaic representing Rome. The bull was last restored in 2017.

Emmanuel Conte and Marco Granelli, from Milan city council, said the arcade’s “lucky spot” had become worn out over time. “The gallery is a living heritage site, which can wear out precisely because it is loved and frequented,” they added.

Galli said he was proud of his work and would like to “encourage young people to take up this profession, because Italy is very much in need of male and female restorers”.

He added: “I know it’s a demanding job, because you have to travel from site to site … but it is also a job regarded in Italy as a privilege.”