Glass Identification - Post here for all ID requests > Resolved Glass Queries
Just bragging - what I bought today!
Quackers:
--- Quote from: Glen on November 06, 2007, 10:16:00 PM ---They're not "straw" (shear) marks though (there is only one of those on a piece and it would be on the interior).
--- End quote ---
Glen, thanks for reminding me about that - I see so many of those marks described as "straw marks" that the term has rather stuck itself into my mind. At least I didn't say that they were anything to do with the hot glass being rested on a bed of straw to cool ::). Is there an acceptable name for those ripple-like marks within the glass to distinguish them from the wiggly surface marks and/or straight mould lines?
Sorry but the more I think about it the more questions come to mind - why would a shear mark only be on the inside? As I understand it they are caused by the cold metal tool touching the hot glass metal (or is that another myth) so shouldn't that appear on both sides of the glass?
Thanks for keeping me on my toes ;D.
Tim
Glen:
Tim - great questions! I will answer them as best I can, but I am sure that someone like Adam Dodds can give us more information too. I must say, upfront, that most of what I have learned about the pressed glass manufacturing process - and especially the features of that process as exhibited on the glass - are things that I have learned from Howard Seufer (ex-Fenton) and also from Adam D.
The shear mark is (as I understand it) almost always on the upper surface (in contact with the plunger). It occurs at the point where the gob of hot glass is cut (the tail end of the gob) and thus falls down into the mould. I suppose the glass maker could attempt to flip the gob to the outside, but I imagine that would be physically tricky. I do know that a glass maker might attempt to toss the tail of the glass to the edge of the gob so that it will re-heat. But mostly, on older pressed glass, the mark may sometimes be seen on the upper surface. Sometimes it is covered by a busy moulded pattern, but on those items where there are large areas of plain glass, it can usually be easily spotted (the Carnival piece "Peter Rabbit" often shows a shear mark in the centre).
Later, the shears had a rounded end to one handle, so that it could be used to rub out the mark. But that wasn't used during the Classic Carnival era.
I believe the marks on the exterior (where the piece is in contact with the mould) are caused by a temperature differential between the hot glass and the metal mould. If the mould is cooler than the hot glass, then settle waves may occur as the hot glass skids along the mould surface. These are wavy lines that curve around the outside of the item. As the glass then gets pressed and starts to move, settle waves sometimes form.
If the mould is too hot, the slightly cooler glass can stick to the mould and make lines that can look a bit like fine cracks. I suspect this is what we are seeing on the Four Flowers Vts. They often feature on those items.
One more mark on the exterior is called a lap mark. I'll quote Howard...it's like a "rolled edge line that looks like the line your fingernail would make in an apple skin....caused by the glass gob hitting the side of the mould before being formed".
oh yes...EDITED TO ADD something I forgot - my article on the Shear Mark.
http://www.geocities.com/carni_glass_uk_2000/ShearMark.html
Cathy B:
Thank you for that explanation, Glen!
Is there a name for the effect that looks like fine cracks on the surface of the glass?
PS - it's good to see you here again! We miss you when you're away.
Glen:
Cathy :hug:
You asked a very good question - I will get in touch with Howard Seufer and ask his opinion.
Thanks, everyone, for the fascinating discussion.
Quackers:
Thanks Glen, I think I'll print that off and keep it somewhere safe! I certainly understand the shear mark location now - but I'm not sure I've ever seen it... wanders off to look at shelves full of glass 8)
If I ever manage to get to a Carnival Glass Soc meeting (they always seem to be on days I'm stuck at work) I'll bring a couple of pieces along for a consultation!
thanks again.
Tim
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version