the black marks are simply impurities that have found their way into the batch - pieces like this are a long way from having any quality, and the inclusion of a little carbon/dirt from the pot or the floor wasn't presumably seen as a problem.
A small carafe like this wouldn't have involved using the gadget - it was blown and then a pontil iron attached to the base in order to finish the top. Gadgets were used on drinking glasses only, I believe, mostly during the last quarter of the C19 - which may have been after this carafe was made - but that date line is my opinion only - as with so many of these smaller utility low grad pieces, accurate dating is not easy.
Attached is a pic showing a similar situation on the neck of a vinegar/oil condiment bottle (which also has bubbles and a snapped pontil).
The carafe might be soda glass - although the books suggest there is a slightly brownish, yellowish or greeny-grey colour if it is. Potash glass looks brighter, is harder and is less plastic, but not a subject I really know. I expect there's a way of differentiating the two.
The carafe is dinky though - and I was going to suggest it might be simply for an individual serving at table - there are records of English examples, with wheel engraving that are this size. But there's a limit to how much information can be assessed from a piece like this, unless you can find a specialist. Age wise possibly the middle third of the C19, which is a bit like say 80 - 120 (a euphemism for I don't really know)