Topic: Anybody heard of skeleton molds?

[Frank]

It will be in the next batch of patents I upload I study, so c1878, but nothing more then I said above, other then a picture (I think)

[Fuhrman Glass]

I think you've finally got it right, multiple fingers with oval openings on the top of them. They are held together with a metal starp that goes around them and keeps them in position. After the parisom is expanded, the fingers are allowed to fall away from the glass. The center of the parisom can initially be made a lot thicker than the other parts of the piece through bubble control and cooling and marvering techniques before it is ever put in the mold, resulting in the center "lenses" being much thicker than other portions of the pitcher.There are multitude of other techniques that could have been employed to get this same result. i.e. picking up oval lenses on the hot parison before the piece was ever put in the mold and blown out. You can cast these in a row with space between them and roll the parison over them ans pick them up, then blow the piece into a "skeleton"/finger mold that would give you the sides, or do the pickup after the piece was initially blown. or the lenses could have been inserted into depressions in the skeleton mold and kept hot till the parison was inflated and picked up the lenses. Final finishing with hand torches and glaziers could have fire polished these areas then.
Or it could have been blown into a thin metal form with the glass coming thru it and then the metal was etched away from the glass after the piece came out of the annealer. I used to work with a company that did a lot of the blowing into metal frames in the 60's when the "Spanish" and "Mediterranean" styles were popular in the US. The glass could most often be easily cut away from the metal when it cooled.
Just a few more ideas to ponder.

[Frank]

The object/mould would be rotated presumably to avoid the texture given the surface of glass by metal moulds, just as an object is rotated in a turn/paste mould.  If the interior of the mould doesn't have a water-retaining surface, maybe the holes inject a bit of air to keep the glass away from the metal?  Or they're simply for cooling the mold, as molds used continuously tend to get too hot.  I read somewhere the other day about molds that had air circulating through them to keep them cool.

I wonder what it means that they were built up of bars.

There is another example in the Study patents that was intended to provide standard shaping for wineglass 1873/676

The bars of the rubber are made of graphite, carbon, &c. and may be straight, spiral, &c. in shape provided that in revolving they describe the contour of the vessel to be formed.

Although this was not specifically named a skeleton mould it does show one of the uses. In this case though the forming bars are fixed.

[Patrick]

Hi,
 Brilliant to see this diagram................

By the diameter of the shaft and the size of the flywheel it must have rotated at a good speed !

Patrick
 

[Frank]

The idea of the flywheel was to to wind the cord again, so each use it would have rotated in the opposite direction. Of course a patent does not mean it was ever used.

[aa]

The idea of the flywheel was to to wind the cord again, so each use it would have rotated in the opposite direction. Of course a patent does not mean it was ever used.

Are you sure? I would have thought it was to create a constant speed of rotation.

[Frank]

Yes, part of the description

The shaft D is then caused to rotate by sharply pulling a cord or strap K coiled upon it. A flywheel H mounted on the shaft serves, by its impetus, to re-wind the cord K

[aa]

Ok, fair enough, but it is just an ancillary purpose of the flywheel to re-wind the cord. The cord is really there to rotate the flywheel!! The reason for the flywheel, surely is to ensure a constant speed of rotation.
Otherwise, you could spin the flywheel by hand and a cord would not be necessary. Indeed, I wonder how long the cord method lasted before they realised you could get just as good a result by spinning the flywheel by hand! Probably less hassle as well.

[Patrick]

Hi,

I think the key to this is the " sharply pulling "   This would get the flywheel going a good speed.  As Adam says the cord would rewind itself immediatly you let go at the end of the pull !!!!!!

Regards, Patrick.

Ps. I sold mt Meccano sets long ago otherwise we could have tried one at Adams.

[krsilber]

Thanks for posting the diagram, Frank! 

After reading the patent, it seems to me the flywheel and cord were meant to rotate the mold smoothly and rewind it.  Pulling a cord once is a quicker, easier, one-step way to rotate the mold than turning it by hand - a single person could set it in motion then put the bubble into the mold.  Or does the bubble have to go in first?  I'm a little confused about the bars, and the mold itself.  Do the bars slide over the glass, forming it that way, or do they grip it, so that the centrifugal motion of the machine expands the glass out between the bars? 

Of course a patent does not mean it was ever used.

  Yes, I've been thinking about that lately.  There must be a lot of patents out there that were never used for commercial production.

One thing I've been wondering about is patents for glass formulas.  It seems like many of them are sort of wishy-washy, saying the formula contains (four particular ingredients) plus additional ones, at the maker's discretion.  This one, for example:  http://www.google.com/patents?id=jpNpAAAAEBAJ&printsec=abstract&zoom=4&dq=1629648
It says, "My invention is applicable to any sand and soda ash mixture with or without other ingredients and the addtion of litharge, borax and manganese is optional."  Two specific formulas are give at the end - is the patent, then, just for those two formulas?

I think you've finally got it right, multiple fingers with oval openings on the top of them.

Tom, thanks for checking in ... it's always nice having another glassblower's ideas, and further confirmation that the distorting/skeleton mold Cummings describes could have been used on the pitcher in the OP.  No doubt the bosses could have been made using other means, but my original question about skeleton molds seems to have been answered.   "Final finishing with hand torches and glaziers could have fire polished these areas then."  Any idea when the use of hand torches began?  What's a glazier?

BTW, do you all remember the vase that apparently has the same design as the pitcher?  I FINALLY heard from the owner a week ago that it is smooth on the inside, with no depressions behind the bosses.  Perhaps that means it wasn't made using the same type of mold, or maybe with the thicker glass there that Tom was talking about they just don't show up because that part wasn't really blown into shape, as the thinner glass was.