Topic: cracked Ysart

[tropdevin]

Do any of our glass maker colleagues (esp. Scottish ones) know why Ysart weights are relatively prone to cracking ( example)?  Was it a poor annealing process, or incompatible coloured glass, or what? I see a higher proportion of cracked weights from Ysart than any other maker.

Alan

[Frank]

Annealing of Monart was not particularly good. This was probably because the Ysart's used and made their own batch, and imported colours - the glass technologists at Moncrieff were not privy to the recipe and in any case did not  deal with coloured clear/mixes. . Salvador considered paperweights a waste of time so would have not taken any interest. Paul took a personal interest in technology and would have worked to resolve that once Salvador was out the way and he had control over the process.

Vasart's annealling lehr made from corrugated iron and a milk crate conveyor, was accidentally better which is why annealling cracks do not show up in Vasart.

So a crack could be a useful dating tool

[Cathy B]

An earlier thread on the subject is here.

[tropdevin]

Thanks both - that is helpful.

Alan

[tropdevin]

Here's another one! This time it looks like a translucent orange ground.

Alan

[KevinH]

Franks said, with use of  and  ,

... which is why annealling cracks do not show up in Vasart. ... So a crack could be a useful dating tool.

I have conisidered that point, too - as a serious piece in the "as-yet-unfinishable-jigsaw" of weights possibly made by Salvador. I have an example of an Ysart weight that seems to be early Vasart, with a crack right through the centre, top to bottom and with no blemishes on the surface, so unlikely to have been caused solely by knocks and bumps.

Maybe pre-war annealing problems could be a factor in showing my weight to be earlier than I currently think. And if so, other clues, such as the canes and finishing, might help to push other weights back into the 30s rather than "early Vasart".

On the other hand, perhaps it is only in the last decade that any general Vasart weights (as opposed to really unusual ones) have been seen as something that can generate some reasle profit? Maybe before that, many cracked Vasart weights were known but just binned because they had absolutely no resale value and very little academic interest to save them as discussion and reasearch items?

I'm still thinking about this sort of thing on occasion!

[RAY]

here's my cracked ysart, the cracks seem to appear from the pontil mark,  on this one it has been hand chipped away, now then, if they were to hand chip the pontil away and if they leave small cracks surely over time the cracks will get bigger until they meet due to different temps, i know when i got this one i marked a crack with a felt pen, and now the crack is about 4-6mm longer , so one day it just might drop apart

click image

[Mod: Aug 2011. Photobucket links point to real photos but not to ones we would expect! Therefore, all have been deleted.]

[aa]

I think "annealing crack" is a misnomer. Cracks such as these can be caused by a number of reasons. The most likely is that the colours used are incompatible and have different co-efficients of expansion. In such a case no amount of annealing is going to make any difference. Other reasons can be that the annealing cycle has not been controlled properly, ie the glass has been cooled down too quickly. Alternatively the glass may have been too cold before it was put in the lehr and if this was the case, no amount of annealing would make any difference. If the piece is put in at the correct temperature and then the door of the lehr is left open for too long putting in the next few pieces, aand particularly if there is a draught, then this can chill the outside of the weight sufficiently to crack it. If you open a lehr door and move a piece with a glove or even touch it when you are putting another piece in, this is all it takes to cause a crack. I could go on and on! There are several other possibilities.

I think "stress crack" is a much better term, as the type of crack in Ray's image shows that it has not been annealed properly and there is still stress in the glass.

[Fuhrman Glass]

aa: good explanation. I have had instances that I made a run of thre same piece in a day's production but may have couple that show the type crack you are referring to. Many times the surface tension of a paperweight will keep the inside elements in compression and even though the coeffecients of expansionn may be considerably different, the piece will not crack. The viscosity of the different glasses has a great bearing on this as well.
I have also found that some colors of glass will shift to a different COE everytime you go into the glory hole and reheat it. This can cause a lot of problems if you're not used to using that particular color.
The more lead content that some of the colors had also allowed for the mixing of some colors that is not possible today.
I would be interested in knowing what type of control they used on their annealers prior to WWII and how long they annealed items.

[Frank]

They had a tunnel lehr, see layout diagram halfway down http://www.ysartglass.com/Ysart/Monartglass.htm There is no-one left alive that could answer more about it.