provided is a radiation - curable optical glass fiber coating composition adapted to provide the combination of properties of : enhanced resistance to thermal degradation when suitably cured ; and a viscosity sufficient to provide a surface substantially free - of pitting . the composition is formulated from components including : at least one epoxy silicone monomer or oligomer which is crosslinkable via actinic radiation , or mixture thereof ; at least one thermoplastic resin which is substantially unreactive to actinic radiation and which is soluble or dispersible in component , said thermoplastic resin being present in an amount to provide said composition with a viscosity suitable for application to an optical glass fiber ; and a catalytically effective amount of a photoinitiator for catalyzing the crosslinking reaction of component and which is soluble or dispersible in component or a mixture of said component and said thermoplastic resin . also provided is a method of making the radiation - curable coating composition and a coated optical glass fiber .