This article gives some examples of possible origins of defects introduced in articles due to mould design deficiencies. During the work on a press machine, when the glass gob reaches the mould, the plunger uses its pressing force to oblige the glass to fill all the area between the plunger, the ring, the mould & bottom plate in the minimum time possible. At this point, in a single working phase, the glass item has been formed. However, the article cannot be considered perfectly finished after the pressing phase, since one or two "burning" phases are usually necessary to eliminate irregularities on the surface of the item, also slowing down cooling. The defects that can appear on items are caused by inconsistencies in the assembly of various parts of the mould & limits in design.
