We bought this 1925 Craftsman house and were told this fireplace was original (We put the gas insert in, though). It seems like it is concrete with the tile pattern and texture drawn in and then some sort of treatment to give the rainbow effect. I am wondering what this effect is called and if it is in fact original to the 1925 era - there were lots of later updates to the house so am not really sure what era it is from. There are some cracks which we would love to repair but don't even know how to start describing it or the treatment. Anyone know what this is? Thanks!