Once satisfied with the thickness of the end, take the glass out of flame and continue to rotate for several more revolutions, then blow. As you blow, carefully watch the glassif it is expanding too great in size or expanding too quickly, stop or slow down your blowing. If you see no movement, either you are not blowing hard enough or the glass is already too cool. If you end up with an end as pictured, it means that ether you were not adequately heating a sufficient amount of the bottom surface, or you let it cool too long before blowing. If the glass is not overly thick at this point, you can reheat and try again.
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