Based on the observations of architectural historians and architects, it is clear that many masonry buildings in the 17th, 18th, 19th and even the early 20th centuries were commonly coated with a red paint made from lime, hide glue, or linseed oil.  While it is commonly assumed today that colonial brick buildings were unpainted, by closely examining areas of protected brickwork, such as under porches or behind shutters, it is often possible to find surviving traces of red paint.  What was the purpose of these coatings?  One theory holds that they were used to either protect the lime in the mortar as it slowly cured to its full strength (a process that could take years).  However, evidence has also been found that brick buildings were often repeatedly painted with these coatings, strongly suggesting that the paints also served a decorative function.