“For more than 350 years, monsoon rains in Agra, the bustling city where the monument sits, were enough to wash dirt off the structure’s walls. But pollution has worsened over the last couple of decades, and parts of the marble facade have turned yellow and black. … Cleaning the monument is time-consuming and challenging. To remove discoloration, workers suspended on scaffolding are caking Fuller’s earth – a mud paste that absorbs dirt, grease and animal excrement.”