Abstract: This ceramic composition is produced from a mixture of yttrium oxide and heavy rare earth oxides having an atomic number of from 64-71 in selected proportions for the construction of crucibles and the lining of molds employed in making castings of reactive metals, such as titanium and alloys thereof. The elements utilized in the composition impart a minimum of contamination to the molten metal during the melting and casting phases and are produced from an ore with only the refinement steps necessary so as to secure maximum economy and yet insure the production of castings of the highest quality.