Sarah,

Ghost mold seams will be here past Christmas.  The are the lines left by a
parison mold that shapes the glass before it is transferred to the blow
mold.  If you look at any bottle of products that you are currently using
you can generally see them.  The off-center circle on the bottom of bottles
and jars is a ghost mold seam.  The bottle you have that is solarized was
probably made on a semi-automatic bottle-blowing machine because manganese
did not work well as a decolonizer in tank furnaces that were used to feed
fully automatic bottle-blowing machines.  For further discussion of
machine-made bottles see:

George L. Miller and Catherine Sullivan
1984  Machine-Made Glass Containers and the End of Production for
Mouth-Blown Bottles.  Historical Archaeology 18(2):83-96.

      This has been reprinted Approaches to Material Culture Research for
Historical Archaeologists compiled by David R. Brauner and is available
from the Society for Historical Archaeology.  It contains 25 articles on
material culture research and is a bargain at $25.00 plus shipping.

      I have a bibliography on machine-made bottles and a paper titled
"Dates for Suction Scarred Bottoms: Chronological Changes in Owens
Machine-made Bottles" by myself and Tony McNichol for anyone that is
interested.

George L. Miller
URS Corporation