A process of forming a calcium-magnesium-aluminosilicate (CMAS) penetration resistant coating, and a CMAS penetration resistant coating are disclosed. The process includes providing a thermal barrier coating having a dopant, and exposing the thermal barrier coating to calcium-magnesium-aluminosilicate and gas turbine operating conditions. The exposing forming a calcium-magnesium-aluminosilicate penetration resistant layer. The coating includes a thermal barrier coating composition comprising a dopant selected from the group consisting of rare earth elements, non-rare earth element solutes, and combinations thereof. Additional or alternatively, the coating includes a thermal barrier coating and an impermeable barrier layer or a washable sacrificial layer positioned on an outer surface of the thermal barrier coating.