Mysterious stains on St. Louis' Gateway Arch prompted a tricky testing procedure. Please LIKE & SUBSCRIBE if you enjoyed! http://bit.ly/1G7yMhG **More info & videos below** For full episodes, check out http://www.scitechnow.org/ The iconic St. Louis gateway arch, an engineering wonder that towers high above the skyline, is now 50 years old. Discoloration on the stainless steel exterior has building doctors climbing 630 feet up the arch to examine the cause of some of those mysterious stains