The disclosure relates to logging sensor or tool including an electromagnetic radiation source operable to emit at least one wavelength of electromagnetic radiation, a detector operable to detect the wavelength of electromagnetic radiation, a polycrystalline transparent ceramic component transparent to the wavelength of radiation, and a flowline between the electromagnetic radiation source and the detector having at least a portion of a wall formed from the polycrystalline transparent ceramic component, the flow line operable to permit the flow of a drilling fluid. Such a sensor may be used in a logging while drilling or measuring while drilling apparatus. The also disclosure relates to a wireline measurement apparatus including a sensor comprising a polycrystalline transparent ceramic component. The disclosure further relates to a cast logging sensor or tool component comprising a polycrystalline transparent ceramic component, wherein the sensor component has a shape not obtainable from a single crystal using machining techniques.