They look like an inkwells, but what for?

It is what they call a Betty Lamp. Animal fat for fuel and you lay a wick in the spout area. The pointed piece is driven into a wood beam and the lamp hangs from it.

These lamps were very common in Germany  - I guess they came to the US with the Pensyvannia 'Dutch' immigrants..

The first documented betty lamps seem to have come with the colonists at Plymouth in the early 1600s.   Apparently, Captain John Carver brought a Dutch betty lamp that he had purchased in Holland while the Puritans were living there before coming to the Americas.   What he brought may have been a crusie rather than a true betty, but the two are intimately related, the betty having a single improvement over the crusies of Scotland and Ireland, or the cressets of the Channel Islands.  None of these is particularly more sophisticated than the stone oil lamp found in Lasceaux (around 17,000 BC).

The hanging system for these lamps predates the (apparently) German improvement of an internal support for the wicking (any drops of the fat or oil dropped back in the reservoir instead of on the ground).

Known as a Frosch Grubenlampe in Germany (literally Frog miner's lamp - not sure if Frosch refers to the shape or a maker) used in the stone and ore mines, and even in 'dry; coal mines.... do a Google image search for Grubenlampe, and you get miners' saftey lamps, add Frosch and you get hundreds of images of this type... I bought one on ebay.de last year, but it turned out to be a moderen replica - as you say the type has been around for a long time - Roman ones were usually made of clay, but cast ones from this period do exist as well...
I guess the needles on the chains (in the first image) are to adjust the wick while it is burning....
You can still buy ones new in clay for about 10$ - see: http://www.harzplus.de/shop/catalog/product_info.php?products_id=185 although this one is for burning aromatic oils, not for light....