The main cause of pinholes in pottery is air bubbles created by gases in the Glaze or Clay body. Had the troubles begun with a new batch/bag of clay? Thank you! Yes, the arrows point to a bubble form and pinholes and when I sand it there is no glaze under. Yes, this is a new bag of clay. Polishing finalizes the connector endface and cleans the surface, which has a direct impact on optical performance parameters such as insertion loss, return loss, and ultimately bit-error-rate for ove all network performance. For example, while crawling is often seen as undesirable, it is a characteristic. Pinholes are one of the most common imperfections that occur during or after glazing pottery. In order to do so, you need to understand what causes pinholes in.