I recently purchased a brick, ranch style house that was built in the 1950s. The exterior has black marks all over it and I'm trying to figure out what they are, if they pose a risk, and how to remove them, if possible. Most Google searches indicate that black marks on brick are typically some sort of algae or mold. These seem different than anything I'm able to find examples of. In some cases they seem to just sit on the surface of the brick, while others seem to either eat slightly into the brick or even protrude from the brick. Any ideas as to what these marks are?