Dating black glass bottles
Until the 19th century the method of blowing a piece of molten glass with a pipe and some other simple devices into the shape of a bottle was the only way to produce wine bottles.There was of course the method of casting, where you simply heated the glass to a higher temperature and then let the liquid glass run into a mold where it cooled down.The color is often a dark green, but there is almost any color possible, you can even find a few clear glass bottles.
Because of the method, the size and shape of free-blown bottles vary greatly.Since the process of blowing includes rotating the piece of molten glass, you can often (not always) recognize some circular patterns in the glass that result from the rotation.But the molds where rather roughly shaped and the extra amount of heating material needed to liquefy the glass made the method of casting unsuitable for the production of higher numbers of any containers made of glass.You could also blow the molten glass into an outer mold, so that the shape was assumed quickly and the variations between two containers became smaller.
This does not refer to the shape of the bottle, but to the way the bottle was made.
Madeira bottles tend to come in many shapes and sizes.