Plumbata
Well-Known Member
I found Joe's thread, here are a few relevant images (thanks Joe!):
Here is a scaled-down model of a glass-works that Joe posted. Looks more TOC-ish and the model molds look like later cast iron ones, but I don't see why similar devices couldn't have been used with interchangeable brass molds in earlier years.
Another idea is that the molds (molds plus shell) may have been hinged along the bottom instead of the sides. I certainly don't have any examples to study, but if any of you have some Lafayettes or other early flasks, please check the thickness of the seam which goes across the bottom and up the sides. If it doesn't vary much in thickness, as with later blown bottles where the seam is thin on one side (hinge side) and thicker on the opposing side, then we might assume that the molds were used/operated in a different manner.
I forget the correct terminology, but Copper alloys have a great "capacity" for heat energy, and unless I'm mistaken the capacity is far greater than the considerably less-dense glass. This, combined with the efficiency of the heat-transfer or dissipation of the alloy I would imagine that the entire mold would need to approach very near its melting point before it would fail. Perhaps someone with a background in physics can determine the heat capacity of a unit of copper(brass) versus the energy in a unit of molten glass, and also the energy transferred at the glass transition temperature between molten and solid states (assuming there is a large amount of energy transferred at that stage, as in the transition of ice at 32 degrees to water at 32 degrees).
Perhaps the brass/bronze used would be similar in composition to alloyed naval cannons? To draw this into an analogy to address Chris' points, the gunners operating a cannon knew to let it rest to avoid overheating, and we've heard of machine-gunners urinating on their weapons to prevent or delay overheating. Just as the cannon crew knew the proper interval between shots necessary to prevent overheating and failure, I'd imagine that the glassworkers adhered to some sort of usage/rest system, or if there was a huge order, could have used water to cool the molds. Jeff's useful tidbit shows that 500+ quart bottles per day was the norm, and for a considerably smaller bottle like the Lafayette the number may be higher.
If we assume 600 bottles per day, and a 12 hour workday, then that would be 2 minutes per bottle. If the mold was allowed a minute between removal of the previous bottle and introduction of a fresh gather then I'd bet the mold would be able to cool quite sufficiently, perhaps even with an interval of 20 or 30 seconds.
If you look at the base of the Coventry mold you can see that it is rectangular in profile. Perhaps this was exposed on the bottom of the hypothetical shell and operated as a heat-sink, since the base is where the majority of the heat-transfer from glass to metal would occur, as this is generally where the thickest part of the bottle is.
We really need some good shots of the superficially less interesting parts of the mold.
Here is a scaled-down model of a glass-works that Joe posted. Looks more TOC-ish and the model molds look like later cast iron ones, but I don't see why similar devices couldn't have been used with interchangeable brass molds in earlier years.
Another idea is that the molds (molds plus shell) may have been hinged along the bottom instead of the sides. I certainly don't have any examples to study, but if any of you have some Lafayettes or other early flasks, please check the thickness of the seam which goes across the bottom and up the sides. If it doesn't vary much in thickness, as with later blown bottles where the seam is thin on one side (hinge side) and thicker on the opposing side, then we might assume that the molds were used/operated in a different manner.
I forget the correct terminology, but Copper alloys have a great "capacity" for heat energy, and unless I'm mistaken the capacity is far greater than the considerably less-dense glass. This, combined with the efficiency of the heat-transfer or dissipation of the alloy I would imagine that the entire mold would need to approach very near its melting point before it would fail. Perhaps someone with a background in physics can determine the heat capacity of a unit of copper(brass) versus the energy in a unit of molten glass, and also the energy transferred at the glass transition temperature between molten and solid states (assuming there is a large amount of energy transferred at that stage, as in the transition of ice at 32 degrees to water at 32 degrees).
Perhaps the brass/bronze used would be similar in composition to alloyed naval cannons? To draw this into an analogy to address Chris' points, the gunners operating a cannon knew to let it rest to avoid overheating, and we've heard of machine-gunners urinating on their weapons to prevent or delay overheating. Just as the cannon crew knew the proper interval between shots necessary to prevent overheating and failure, I'd imagine that the glassworkers adhered to some sort of usage/rest system, or if there was a huge order, could have used water to cool the molds. Jeff's useful tidbit shows that 500+ quart bottles per day was the norm, and for a considerably smaller bottle like the Lafayette the number may be higher.
If we assume 600 bottles per day, and a 12 hour workday, then that would be 2 minutes per bottle. If the mold was allowed a minute between removal of the previous bottle and introduction of a fresh gather then I'd bet the mold would be able to cool quite sufficiently, perhaps even with an interval of 20 or 30 seconds.
If you look at the base of the Coventry mold you can see that it is rectangular in profile. Perhaps this was exposed on the bottom of the hypothetical shell and operated as a heat-sink, since the base is where the majority of the heat-transfer from glass to metal would occur, as this is generally where the thickest part of the bottle is.
We really need some good shots of the superficially less interesting parts of the mold.
] I don't remember if the mold was or not.....Maybe if the right person were to ask the right person, they'd allow it...Red has some pretty extensive knowledge of metallurgy,and bottle molds,.... perhaps not as far back as to the dates in question here though....
