I can't see a pontil mark and 5.5 cm is also rather large (it's over a quarter of the diameter of the item!). Are you sure there is a pontil mark and that you are not just talking about the indent for the base rim? The ribs indicate to me that this piece was pressed, but I could be wrong.
Here is a copy of something I wrote for another discussion board
A pontil mark is found when a piece of glass has been attached to a pontil iron or punty for some form of finishing treatment. The item in question is heated and attached to the iron with a blob of molten glass and then it might be shaped at the top or have some form of molten glass decoration applied, anything that requires the item to be worked while it is hot. When this work is finished, the item is cracked off the rod and cooled. This cracking off leaves a raised sharp scar. The scar may be left as is (fairly common on very old pieces or new pieces pretending to be old); it may be heated to smooth out the sharpness, which still leaves a raised lump; it may be ground down to leave a concave indent; or it might be hidden by applying a fresh blob of glass and stamping a pattern. The ground-out indent can vary in quality from irregular and matte to perfectly circular and shiny, depending on how much more work has taken place. These sorts of marks are usually found on blown items, whether free blown or mould blown.
It is very unusual but not unknown to see a ground top rim and any sort of pontil mark. A ground top rim means the item was attached to the punty at the top for final hot finishing (adding stems or bases, for example) or was just cracked straight off the blowing iron. Rims that have been cracked off may also be fire polished rather than ground.
Other types of pontil mark removal are indicated by ground base rims (on pressed items) or or perfectly flat and shiny bases, often but not always on cut items.
The size and finishing of a pontil mark vary, but usually (but not always with pieces from smaller studios) the better the finishing, the better the quality of the item. Finishing adds costs.
Sometimes pontil marks themselves may have what looks like small scars. These occur when there was insufficient base glass to achieve a perfect pontil but the quality of the item was good enough for sale.
Opaque or semi-opaque Victorian era items may have black marks in the pontil mark. This is residue from the punty iron and because it didn't show, it was considered OK.
Rings and ripples are consequences of either blow molding or cooling or both.
Topic: Glass Green Plate - Red and white splashed effect. Sklo? (Read 2549 times)
