According to officials, it wasn’t done by the company the city selected to do it and nobody else claimed the responsibility yet.
Graffiti on Charles Bridge, which restorers began removing on Saturday, disappeared unexpectedly overnight.
“The restorers worked on the site on Saturday until five o’clock in the afternoon. When they arrived at 10:00 in the morning the day after, the graffiti were removed,” TSK spokesman said.
Tests are now underway to determine whether the substance used had damaged the stones of the centuries old monument.
Two foreigners both from Germany were arrested on Monday evening, July 22 while spray-painting a five-meter long and two-meter high graffiti on the Charles Bridge. They were caught in the act after a bystander called the police.
The two mischief-makers have been fined 100,000 Kc each (around 4,000 euros) and ordered to cover up the cost of cleaning and restoration.
The Charles Bridge is currently undergoing an extensive reconstruction that could last for up to 20 years.
Graffiti on national monuments is rare but not unknown: A Japanese tourist in December 2014 painted on an underpass that was part of the National Theater. In October 2014, a French tourist painted teeth and a tongue on the National Theater itself.
The Astronomical Clock Tower has also been damaged by vandals on several occasions.