Just moved into a condo with some interior brick that needs cleaning. The brick is in the kitchen and it appears the developer coated it with a glossy sealant. That developer is unreachable, and my new neighbors are not sure what the covering is. Over time is appears to have lost its sheen and yellowed (see photos). Does anyone know what this coating over the bricks might be, and which cleaning solutions might remove it? So far I have tried soap/water, borax, and acetone with no results.