DETROIT - The exterior of the 13-story Book Building, and it's joined-at-the-hip sibling, the 38-story Book Tower, have been due for a nice bath for, oh, let's say the past 50 years.

The exterior of the buildings have finally been getting a good scrub the past few weeks, by way of a good power-washing performed over the past few weeks by masons from Bricklayers and Allied Craftworkers Local 2 and Ram Construction.

Empty since 2009, the Book Building was purchased last year by Quicken Loans Founder Dan Gilbert and his Bedrock Real Estate arm. Plans call for a future mixed use for the building, a combination of retail, office and residential.

The 13-story building (1917) was the first to be erected by local real estate entrepreneurs and Book brothers J. Burgess Jr., Herbert and Frank. Located north of Michigan Avenue along Washington Blvd., it was mated nine years later when construction was complete on the 38-story tower. The Book brothers also developed the Book Cadillac Hotel across Washington Blvd.

The Book Building is encased in limestone, which is a very porous material, and has certainly absorbed its share of soot and other pollutants over the years, leading to the discoloration.  But it's all being washed away.