Plumbata
Well-Known Member
Excellent stuff people.
Joe thanks for the pic, do you have access to a picture of the back side of the Coventry mold?
I've got a little theory going, hopefully some of you can flesh it out.
The brass/bronze/bell-metal mold HAD to have been cast. It would make sense if the glassworks contracted with a foundry to create not just the raw mold, but also the more intensive section which creates the embossing. Bell-makers/founders were very experienced with mirroring text and it is likely that they took care of this issue for the glassworks before the days of slug-plates.
Now, in the 1st quarter of the 19th century, what entity local to Coventry, CT would have the ability to cast a suitable mold? I'm thinking that the bronze used in bells would possess a melting point far lower than ideal, since it was upwards of 22% tin. In my youth I took a blowtorch to an ancient roman coin (trying to remove crust), and was perplexed when silvery beads of molten tin started issuing forth from microscopic pores in the coin. Lacking analytical data regarding the proportions of the ingredients used, I will just assume that actual bell-metal with high-tin would be avoided, as potential beads of molten tin flowing inside a bottle mold would be less than ideal.
The data I desperately desire is an analysis of the metals used in early American brass/bronze cookware which was intended to be used at high temperatures. The bottle molds must have been made from a blend understood to withstand higher temperatures. We all have seen antique cast brass pots, pans, etc., but I have no knowledge of early American cookware foundries. Do any of you know about early eastern cast cookware? I'd wager that a cookware foundry created these molds, and a table of the alloy formulas used in the production of high-temp cookware back then would likely include the formula used for the creation of the mold. Do any of you have access to such data?
Now, regarding the "warming" of the molds and the ideas postulated for and against this idea , I think that the properties of heat transfer were known to the glassworkers, and with their desire to be efficient and productive, the mold would not likely have been reheated between use, though I don't see why it wouldn't be heated before beginning production for the day, which is what I thought Chris was getting at.
I want a picture of the backside in order to support or discard this next postulation; the thin-walled molds were likely housed within a larger insulated shell, perhaps stuffed with asbestos or filled with porous plaster of paris with a recess for the molds. This ability to maintain a reasonable running temperature would avoid the effects of super-cooling and the "locking-in" of fatal zones of stress in the glass; as indicated by Jeff. Since copper and its alloys are superior conductors of heat, insulation of some sort would be expected. The unusual posts and sockets on the rim of the mold look like they were intended to be joined with the other half more "directly" (versus pivoting in a sharp arc on a hinge attached to the 2 halves of the mold proper, if that explanation makes sense), and this would also support the idea that the mold was insulated somehow.
Essentially, if we can hone-in on the composition of the mold we can better postulate how it was heated, insulated, used, etc. More pictures of molds are in order.
Joe thanks for the pic, do you have access to a picture of the back side of the Coventry mold?
I've got a little theory going, hopefully some of you can flesh it out.
The brass/bronze/bell-metal mold HAD to have been cast. It would make sense if the glassworks contracted with a foundry to create not just the raw mold, but also the more intensive section which creates the embossing. Bell-makers/founders were very experienced with mirroring text and it is likely that they took care of this issue for the glassworks before the days of slug-plates.
Now, in the 1st quarter of the 19th century, what entity local to Coventry, CT would have the ability to cast a suitable mold? I'm thinking that the bronze used in bells would possess a melting point far lower than ideal, since it was upwards of 22% tin. In my youth I took a blowtorch to an ancient roman coin (trying to remove crust), and was perplexed when silvery beads of molten tin started issuing forth from microscopic pores in the coin. Lacking analytical data regarding the proportions of the ingredients used, I will just assume that actual bell-metal with high-tin would be avoided, as potential beads of molten tin flowing inside a bottle mold would be less than ideal.
The data I desperately desire is an analysis of the metals used in early American brass/bronze cookware which was intended to be used at high temperatures. The bottle molds must have been made from a blend understood to withstand higher temperatures. We all have seen antique cast brass pots, pans, etc., but I have no knowledge of early American cookware foundries. Do any of you know about early eastern cast cookware? I'd wager that a cookware foundry created these molds, and a table of the alloy formulas used in the production of high-temp cookware back then would likely include the formula used for the creation of the mold. Do any of you have access to such data?
Now, regarding the "warming" of the molds and the ideas postulated for and against this idea , I think that the properties of heat transfer were known to the glassworkers, and with their desire to be efficient and productive, the mold would not likely have been reheated between use, though I don't see why it wouldn't be heated before beginning production for the day, which is what I thought Chris was getting at.
I want a picture of the backside in order to support or discard this next postulation; the thin-walled molds were likely housed within a larger insulated shell, perhaps stuffed with asbestos or filled with porous plaster of paris with a recess for the molds. This ability to maintain a reasonable running temperature would avoid the effects of super-cooling and the "locking-in" of fatal zones of stress in the glass; as indicated by Jeff. Since copper and its alloys are superior conductors of heat, insulation of some sort would be expected. The unusual posts and sockets on the rim of the mold look like they were intended to be joined with the other half more "directly" (versus pivoting in a sharp arc on a hinge attached to the 2 halves of the mold proper, if that explanation makes sense), and this would also support the idea that the mold was insulated somehow.
Essentially, if we can hone-in on the composition of the mold we can better postulate how it was heated, insulated, used, etc. More pictures of molds are in order.
