An organic solvent based slurry composition for making an environmental barrier coating, the slurry composition comprising: at least from 6.8 wt% of a solvent selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, acetone, methyl isobutyl ketone, methyl ethyl ketone, toluene, ethylbenzene, propyl benzene, methoxybenzene, heptane, octane, nonane, decane, xylene, mineral spirits, naptha, tetrahydrofuran, ethers, and mixtures thereof; at least from 3.9 wt% of a primary material; wherein the primary material is a primary transition material and is a rare earth disilicate; and from 0.01 wt% to 20 wt% of a slurry sintering aid, wherein a sum of the solvent, the primary material and the slurry sintering aid is equal to or less than 100 wt% of the whole slurry composition, wherein the slurry sintering aid is a composition that: dissolves in the primary material at a sintering temperature of the primary material; increases a rate of diffusion of the primary material during sintering such that surface area reduction occurs at lower temperatures than would occur in the absence of the slurry sintering aid; and wherein the slurry sintering aid for use with the primary transition material is selected from the group consisting of iron oxide, carbonyl iron, iron metal, iron hydroxide, iron carbonate, iron oxalate, and solvent soluble iron salts. at least from 6.8 wt% of a solvent selected from the group consisting of methanol, ethanol, propanol, butanol, pentanol, hexanol, heptanol, octanol, nonanol, decanol, dodecanol, acetone, methyl isobutyl ketone, methyl ethyl ketone, toluene, ethylbenzene, propyl benzene, methoxybenzene, heptane, octane, nonane, decane, xylene, mineral spirits, naptha, tetrahydrofuran, ethers, and mixtures thereof; at least from 3.9 wt% of a primary material; wherein the primary material is a primary transition material and is a rare earth disilicate; and from 0.01 wt% to 20 wt% of a slurry sintering aid, wherein a sum of the solvent, the primary material and the slurry sintering aid is equal to or less than 100 wt% of the whole slurry composition, wherein the slurry sintering aid is a composition that: dissolves in the primary material at a sintering temperature of the primary material; increases a rate of diffusion of the primary material during sintering such that surface area reduction occurs at lower temperatures than would occur in the absence of the slurry sintering aid; and wherein the slurry sintering aid for use with the primary transition material is selected from the group consisting of iron oxide, carbonyl iron, iron metal, iron hydroxide, iron carbonate, iron oxalate, and solvent soluble iron salts. dissolves in the primary material at a sintering temperature of the primary material; increases a rate of diffusion of the primary material during sintering such that surface area reduction occurs at lower temperatures than would occur in the absence of the slurry sintering aid; and wherein the slurry sintering aid for use with the primary transition material is selected from the group consisting of iron oxide, carbonyl iron, iron metal, iron hydroxide, iron carbonate, iron oxalate, and solvent soluble iron salts.