This paper compares melt processed calcium aluminate fibers from two technologies in terms of their optical and structural properties. Strong amorphous fibers with a modulus 15-16 Mpsi (vs. 9-12 Mpsi for silica fibers) can be drawn from quaternary, low-silica calcium aluminate melts with 42-44%/wt. Al2O3, <6% SiO2, and <5% MgO, and from quaternary, non-silica Ca aluminate melts with 46% Al2O3, 4% MgO, and 14% BaO. These fibers have excellent structural properties. Amorphous Ca aluminate melts with 51.5-80.2% Al2O3 (both with and without silica) have much lower viscosities. They cannot be drawn from supercooled melts, but can be spun, by inviscid melt spinning, whereby a low viscosity jet is ejected into propane, affording chemically induced jet stabilization. These fibers were weaker, but were found to have sapphire-like infrared transmission spectra. A carbon sheath from the pyrolytic decomposition of propane was formed on the surface of most spun fibers. It acted like a hermetic coating and was found to significantly enhance the hydrolytic stability of the fibers.