Tungsten powder is used at Selmet Inc. in the prime coat for titanium investment casting. This metallic layer must be fired and co-sintered along with the rest of the shell made with more traditional investment casting materials. Minor additions of nickel and iron impurities to tungsten powder are shown to greatly enhance sintering at low firing temperatures. Dimensional changes and fracture toughness are characterized as a function of impurity level and are used to characterize and improve tungsten slurries at Selmet Inc.