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Author Topic: Anybody heard of skeleton molds?  (Read 6688 times)

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Offline Ivo

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Re: Anybody heard of skeleton molds?
« Reply #10 on: March 11, 2008, 08:05:54 AM »
In glass pressing the trick is to completely enclose the glass in the mould so it cannot go anywhere else but in the mould. For this the plungers need to have a shape which can be retracted - hence the design limitations of pressed glass. The pressing takes considerable force. For making hollow vessels, two moulds are used, and parts assembled. The difference between thick and thin parts is due to the specific press mould.

In mould blowing the bubble is blown out in a wet wooden mould which is usually hinged; the contact vapour ensures that the mould does not burn. The bubble is turned inside the mould, the result is a uniform, smooth shape and an even, thin wall.

The alternative is a still mould, which is made of cast iron and is always hinged. The outside pattern is worked in the mould, and the bubble fills the space and takes on the outside decoration. The pattern can be felt on the inside of the finished product. The wall thickness will be uniform.

I am convinced your lens vase is pressed. The mould is heated to prevent contraction marks or striae. The better the temperature matches, the better the product. One of the reasons early pressed glass is decorated all over is the limited temperature control available at the time.
Ivo
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Offline Frank

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Re: Anybody heard of skeleton molds?
« Reply #11 on: March 11, 2008, 09:04:55 AM »
Illustrating the matter of temperature control.

Here is an excellent example of the impact of having an iron mould that is too cool, in this case the effect has been used to create a randomised pattern. Today it is done to produce glass looking exactly as it was before more sophisticated controls were available but at the time the method was first used it was just the only way.

English: http://www.lamberts.de/ecathedr.htm
Deutsch: http://www.lamberts.de/tk.htm
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #12 on: March 11, 2008, 10:10:45 AM »
Frank, nice effect with the cooler metal!  (Metal metal, that is ;))  Isn't glass just a fascinating medium?  Whoda thunk it would cause a texture like that?

Ivo, those are great explanations, but most of that I know already about pressed and mold-blown glass.  I might add that some "turn molds," your second category, are iron as well, but coated with a baked-on cork or sawdust mixture to hold water for the steam - hence their other name, paste molds.  The purpose of the steam is to keep the glass from touching the mold, so it remains nice and smooth.  This part about press molds I don't get, though:  "For making hollow vessels, two moulds are used, and parts assembled."  Do you mean two (or more) parts are used?  Why would you use two moulds?  

As far as I know, Steuben didn't make any pressed glass.  So assuming Corning's ID is correct, this was blown.  This is supported by the fact that the lower half of the pitcher is fluted, waisted, and of uniform thickness.

Christine, your piece is pressed, and that's why you can't feel any indentations on the inside.

This type of design, with the thicker medallions, seems pretty uncommon.  Given Carder's propensity for innovation and experimentation, I think we have to consider the idea that these were made using uncommon techniques.
Kristi


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Offline Frank

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Re: Anybody heard of skeleton molds?
« Reply #13 on: March 11, 2008, 10:20:23 AM »
One mould for the inside (plunger) and one for the outside. Both can be patterned.

I cannot think of any method of making the 'medallions' in a blow mould that would defy the laws of physics - so if Corning 'never' pressed glass then you can rule them out. However, you could contact them while they still exist and ask them. I see no reason why an operation that has been as innovative would eschew the the use of pressing to achieve a particular desired effect, at the prices they sell the work for the cost of making a mould for a short run is not prohibitive.
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #14 on: March 12, 2008, 01:49:14 AM »
American cut glass of this time (1905-1912, according to the Corning Museum) and this quality was rarely done on figured, pressed blanks.  They were used by some companies in the later ABP, but for a poorer quality product directed to a different market.

The pitcher and the Steuben/Hawkes vase I posted a link to in post 3 both have ribbed/paneled/fluted lower halves that are narrower than their bases.  It seems like it would be tough to draw these in after they were removed from a press without affecting the ribbing.  I really don't think these were pressed.

I've already admitted I'm not a glassblower, but I don't see why you couldn't have some thick glass coming out openings that when cooled (by compressed air for example) would cease to expand while the rest of the parison inside the mold stayed warm enough to continue stretching and filling the space.  Perhaps the mold was thin around the windows, and therefore cooled more quickly than the rest.  With a paste mold you wouldn't have the problems of direct contact of the glass with the metal.  I'm not saying this is the case - I don't know - but to me there must be an explanation more plausible than that these are pressed.

"...Corning 'never' pressed glass..."  Corning certainly did press glass, still does!  Steuben didn't.
Kristi


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Offline aa

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Re: Anybody heard of skeleton molds?
« Reply #15 on: March 12, 2008, 08:47:29 AM »
Now that the Corning site is back up, can you post a link to a better image?

From memory, these pieces were made at a time when Carder was interested in creating in glass the deep engraved qualities found in historic rock crystal vessels and I believe that your ewer, which from memory is quite an important piece, is probably one of those items. he had access to superb cutters and engravers, and it would not have been beyond their skill to work a very ordinary blank into something like this, lenses included. ie the lenses could have been carved in and polished up. That is not to say that this is how it was done. However, I am sure that Corning will have the answer.

I think it is highly unlikely that skeleton moulds, interesting though they may be, had anything to do with it.
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Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #16 on: March 13, 2008, 01:34:11 AM »
That answer I will readily accept and agree with.  It was my first thought upon seeing the pitcher, before reading in the Gardner book that it was made using a skeleton mold - and from there, my imagination took over.  I should have known better than to believe what was written there, since it also says it's probably a Stevens and Williams prototype of a Carder piece. 

(I'm still curious about skeleton molds, though.)

The description in the museum for the piece says it's engraved in the rock crystal style (although I'm used to thinking of rock crystal engraving as entirely polished, while this isn't) - your memory serves you correctly!

I still couldn't find a photo of it on the CMOG site.  I found one of the Steuben/Hawkes vase in a similar vein, though.
http://www.cmog.org/collection/detail.php?t=objects&type=all&f=&s=steuben+hawkes&record=7

I'm out of town right now, but tomorrow I can post a larger photo of the pitcher, though it's the same photo.

I have 100s of photos I took at CMOG, some of which turned out OK in spite of the dim lighting.  Do you (whoever's reading this) think people would like to see a few?  Would this be the proper part of the forum to post them?
Kristi


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Offline KevinH

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Re: Anybody heard of skeleton molds?
« Reply #17 on: March 13, 2008, 01:52:07 AM »
Posting images taken by you within a museum may be ok, but you should check first that the museum will permit your personal images to be shown via a public internet message board.

If it's ok, then the best course of action is to set up a separate User Gallery in the GlassGallery (such as "kristi-cmog") and simply post an explanatory message in here with a link to the gallery.
KevinH


Offline Lustrousstone

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Re: Anybody heard of skeleton molds?
« Reply #18 on: March 13, 2008, 07:03:48 AM »
Perhaps a skeleton mould is simply one that forms ribs, optic or other


Offline krsilber

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Re: Anybody heard of skeleton molds?
« Reply #19 on: March 14, 2008, 10:43:17 PM »
Thanks, Kev!  Will do.

Christine, I can't say for sure, but it seems from the two references I have seen for it, it's somewhat different from your normal mold types.  I'm getting Gardner's book from the library, so at least I'll finally be able to read the whole paragraph about them that he wrote (FWIW).
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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