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Author Topic: Anybody heard of skeleton molds?  (Read 6694 times)

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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #20 on: March 17, 2008, 11:43:07 PM »
I don't necessarily want to revive this topic, but I did tell Adam that I would post a better image of the pitcher (though it's been several days, and I don't know if he'll see it).

http://glassgallery.yobunny.org.uk/displayimage.php?pos=-9394
detail:
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-9393

Here's also the Hawkes vase with similar round bits (I suspect the Steuben pitcher above was also engraved by Hawkes, but wasn't marked).
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-9408
http://glassgallery.yobunny.org.uk/displayimage.php?pos=-9407
Looking at this one, I'm still a little tiny bit skeptical that the "bosses," as CMOG calls them, were all done by engraving alone.  It's hard to tell for sure, but the surrounding glass looks quite a lot thinner, and like it was formed in a mold (blown, not pressed!).  The ribbing extends right up to the bosses, and I don't see how you could get the thickness required for engraving them, and have the ribbing molded like that.

But maybe this subject has been beaten to death already...I just wanted to follow through on my promise to post another photo. :)

Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #21 on: March 18, 2008, 04:55:12 AM »
Aha!  More support for my opinion that these were made by a special mold...

I just got back from the bookstore.  While browsing, came across a description and photos of a type of mold that was described as being used in the making of "rock crystal" type objects, and it had little gizmos that looked like they were used to make bulges.  There was also an original drawing of a vase that looked like it would have had bosses.  I'm distressed, dismayed and distraught, because I can only remember that the gadget started with "dis-"!  It was used to shape the parison before it went into the final mold.  The book is A History of Glassforming, by Keith Cummings, if anyone happens to have it.  I didn't buy it, I'm going to look for a used copy.

Also picked up British Glass 1800-1914 -awesome book!  Incidentally, they talk about skeleton molds in there, but they show a different thing than Gardner was talking about, or Webb patented.
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline Frank

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Re: Anybody heard of skeleton molds?
« Reply #22 on: March 18, 2008, 10:01:51 AM »
Scanned through some material on moulds and pressing machines without finding any term starting ''dis..."". There are a couple of detailed description of some machines here. Patents tend not to use many "technical" names and these probably came into being when people made and used the machinery. But is could be part of a feeder system, there are several. Or part of one of dozens of different types of machine, let alone individual makes of machine. The patents are not easily digestible but they do give a more thorough description than most books.

http://www.ysartglass.com/Moncrieff/Patent/Patuk320034.htm
http://www.ysartglass.com/Moncrieff/Patent/Patuk320033.htm

and here is a catalogue of machines, with less description but more easily digested:
http://www.ysartglass.com/Moncrieff/MoncrieffMonish.htm
Frank A.
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #23 on: March 18, 2008, 07:39:26 PM »
Thanks for the effort, but those are all machines, and they came into use after these were made (generally 1890-1915, but the pitcher ca. 1910 - I should have mentioned that).

I finally found an image and description of the pitcher in another book I have, Sinclaire and Spillman's Complete Cut and Engraved Glass of Corning.  I thought I'd seen it somewhere!  "Its raised areas were molded in the blowing rooms; its decoration is stone engraved.  The Steuben Glass Works was one of several American companies that made such blanks."  And another quote from Spillman's The American Cut Glass Industry:  "Hawkes and some other firms advertised extensively that they used only blown blanks".  I don't know how late they kept making this claim, as in the 20s and later they did cut/engrave some pressed glass, but that was after the ABP.

Now will you believe that the pitcher and vase weren't pressed?

You can contrast these American examples with somewhat similar English ones, pl. 239 and 240 in Hajdamach.  The English ones were cut to shape, and you can see how that was possible on the very thick blanks.  The one on the cover in the middle is intriguing because it has that cameo band that's deeper than the surrounding glass; I suspect that one was partly molded into that shape.

Found yet another example in my photos from CMOG!
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline Frank

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Re: Anybody heard of skeleton molds?
« Reply #24 on: March 18, 2008, 08:34:08 PM »
Blowing machines output would still be described as blown blanks, fully automatic machines were a bit later on the market. The earliest machines just did the blowing part, the rest of the operation was manual. Feeder machines to the parison to the mould taking another step out of the way. Look for an early text on Glass Technology, say 1910, to get an idea of the state of the art of the time. I mostly used Cousen which is relevant to c1920 and is something of a bible. Copies are not cheap, but worthwhile as it is in good clear language and covers US practise too.

As yet I do not have any other such volumes in the database, my own library is the next to go in, but not quickly as I now have to catch up on all the other activities for my sites. If I find anything would good contemporary discussions on all the different ways of blowing I will let you know. Later texts tend to omit outdated technology.

Some possibles I don't have:

GLASS MANUFACTURE, ROSENHAIN Walter, 1908
Elements of Glass Blowing. Waran, H. P. 1923

Unfortunately most of the best material is in Journals or in German, the former would need to be consulted at Rakow or other technology libraries.
Frank A.
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #25 on: March 18, 2008, 09:07:37 PM »
I was just a week or two ago asking in the Elegant and Depression glass forum I'm a part of whether machine (non-hand powered) presses were adopted by Elegant glassmakers (e.g. Heisey, Cambridge, Fostoria), and evidently they weren't.  I've never seen any mention anywhere of mechanization of ABP glass blowing, and I'm positive I would have come across it if it were in use.  The industry was proud of its handmade wares, and even the hand-pressed blanks made by some ABP companies after 1900 were only used for glass geared toward a cheaper market, with lower-quality glass and simpler patterns, not museum pieces.

I doubt you will find any information that will convince me the pieces posted in this thread were made on the rod, with human breath.

I am interested in the conversion to mechanization, though.  It's all fascinating!  Next time I go to Corning I'm going to have to set aside a week just to hang around Rakow, soaking up all the info I can.
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline Sid

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Re: Anybody heard of skeleton molds?
« Reply #26 on: March 19, 2008, 02:45:47 AM »
Kristi:

Gardner's discussion on the use of a skeleton mould has nothing to do with the lenses that you are so interested in.  He is talking about the process of making vertical indentations or ribs in blown glass.  He then uses the lovely blown pitcher, that started this discussion, as an example because of the identations on the lower half of the pitcher not the lenses.  This is right in line with Hajdamach's thinking.

To figure out how the lenses were made, a person knowledgable about glass production needs to get their hands on that pitcher and examine it in detail.


Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #27 on: March 19, 2008, 04:18:32 AM »
Gardner's description is about the general working of a skeleton mold, and doesn't go into the bosses, but it's the basic idea that's important.

I just got Gardner's book from the library.  I sat in the parking lot, read the passage, and thought about it.  And I think I figured it out.  Whether you all agree or not is another question!  I have the distinct advantage of having seen a photo of the type of mold this was made with.  The bottom diagram on this page I posted earlier gives a general idea, sort of:
http://www.glassfairs.co.uk/Articles/burmese.htm

(Another somewhat related visual clue I came across was a photo of a vase blown into a metal frame that remained part of the piece.  It was point out the large openings in the frame had large bubbles of glass coming out, and the glass exposed by smaller openings was virtually flat.  Not surprising, but a nice little demonstration of how glass will tend to expand.)

The reason it's called a skeleton mold is because it's not enclosed.  There are simple versions, with a bunch of rods stuck in wood, and these form ribs on the bubble.  The one that made the pitcher is more complex.  Gardner describes it like the skeleton of an umbrella (handle up).  There is a basal plate holding a bunch of pieces of metal upright in a circle, and they are hinged at the bottom, so they fold toward the middle.  Some of them form ribs, but there are also some "arms" that have rings on the end (the one I saw a photo of had heart-shaped ones instead of ovals or circles).  I believe the latter move independently of the ribs.  A bulb-shaped gather just slightly inflated is put in the mold and the ring arms are contracted, "grabbing" and shaping the bosses while the glass is still thick.  As the parison is expanded, these move outward, so there is little pressure on the glass to expand inside those areas.  The bubble is inflated until full size, the ribs are shaped by the other pieces of metal, and then the mold is opened, and all the hinged pieces unfold, releasing the item.

Does my description make sense?  The idea does, but it's worthless to you if I can't communicate it.  I might be able to sketch an example.

I'm no glassblower, but I have watched a fair bit of it, and have a reasonable grasp of the behavior of glass.  I think this would work, and it ties in with all the bits and pieces of information I've gathered.  And most importantly, it fits the glass.  All four examples I've posted in this thread show the same characteristics, ones that can't be explained by any other method mentioned.

Any comments?  Feel free to tell me I'm dreaming...I'll just have to find more evidence! ;D
Kristi


"The most beautiful thing we can experience is the mysterious. It is the source of all true art and all science."

- Albert Einstein


Offline Cathy B

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Re: Anybody heard of skeleton molds?
« Reply #28 on: March 19, 2008, 04:24:54 AM »
Sid,

Great to see you here! I'm still trying to conceptualise these things. Would that be what they call a dip mo(u)ld to make optic ribbing? Or is it more that at some stage the gather would be blown into a ribbed former?

Kristi: I've just seen your reply, which would imply a rather complicated form of the latter.


Offline Frank

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Re: Anybody heard of skeleton molds?
« Reply #29 on: March 19, 2008, 09:28:52 AM »
A dip mould is used by glass-blowers to perform basic shaping before blowing is completed, although I suppose there is no reason it could not be used to create a final shape to part of the vase. It is also used to create striping in marvered enamels. It is usually one piece and can be wood or iron. Bronze would be an expensive material but excellent for very fine detail and totally wasted on a dip mould.

The Ysart's at Vasart also used spoked wheels to form wavy edges on the rim.

The main pointer to a piece being mould rather than free-blown is the finish of the base as mould blown would not use a punty, of course if polished flat there would be no evidence left if a punty had ever been used.

The discussion may have lost focus on the lens forming, but is still interesting and useful. Do check out the earlirer discussions on moulds in the Archive forum.
Frank A.
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