Pull-through defects inspection methods using phosphor or sodium lamp in glass-lining

Concerning the pull-through defect, which is a sort of defect of the glass- lining, the following two inspection methods were investigated. One inspect ion method is to detect the fluorescent pull-through defect by adding a flu orescent substance to the ground coat. Another inspection method is to dete ct the difference in color between the pull-through defect and the cover co at under a sodium lamp, as a monochromatic light source. This latter method utilizes the difference in the absorption coefficient of the light of the sodium lamp between the pull-through defect and the cover coat. In ease of the luminescence substance addition, the fluoresence is not detected after 3-h firing and the cost of products increases 20% because of the expensive luminescence substance. Therefore it is difficult to apply the luminescence substance addition to the inspection method. In case of the phosphor addit ion, the fluorescence is detected after long firing and the cost of product s increases under 0.5%, In ease of using the sodium lamp, it is necessary t o take the conventional light source or 450 nm monochromatic light source t ogether with the sodium lamp to distinguish between the pull-through defect and a large bubble. The phosphor addition and the sodium lamp utilization are useful as a pull-through defects inspection method.