Radiation curable compositions for additive fabrication are described and claimed. Such compositions are particularly suited for investment casting applications, and include a cationically polymerizable component, a radically polymerizable component, a certain type of prescribed antimony-free, sulfonium salt-based cationic photoinitiator, and a free-radical photoinitiator. In other embodiments, the composition may also include a photosensitizer and/or a UV/absorber. Also described and claimed is a method for using a liquid radiation curable resin for additive fabrication with a certain type of prescribed antimony-free, sulfonium salt-based cationic photoinitiator and a certain type of prescribed photosensitizer in an investment casting process.