"Maybe a horn made on or for the continent in the second half of the 19th century? I was told that English flasks mostly have graduations in drams on the charger, chargers made on or for continental Europe got graduations in grains."
I agree with your comments then I reread Riling's description of the horn I referenced above, "The graduations on the charger are scaled from 85 to 100 grains...made for the best French trade." Considering that there are no markings could it have been made for the American trade? Riling's horn was made by Dixon.
I was once told that the green color of the horn was a result of a 19th century (or earlier) process to poison the horn with arsenic to kill insects and prevent decomposition if not properly cleaned for storage only prior to conversion to a horn or other.