Blackwood & Co., London is definitely an ink. The more common ones run anywhere from $40 to $75, but I personally have never seen one like that.
What a beautiful example!
From a dig story: "Last but not least, one of the most beautiful bottles recovered at any of the DIVs was Gary Crist’s recovery of an amazing 12-sided, cobalt bottle. When it was shown to me at the hunt, my first reaction (after being quite stunned) was that it was a master ink because of the pour spout but then I saw the embossing. This reads “BLACKWOOD & Co. / LONDON†on one side and “BY ROYAL LETTERS / PATENT/ SYPHON BOTTLE.†The fact that it had a funky top with the words syphon made me think that it could also be an early seltzer or mineral water bottle. In fact, just recently there was an long article about early siphons in Antique Bottle & Glass Collector magazine. Two other experienced bottle collectors, Ernest Bowers and Jim Dews, both said to me that they thought it was an English ink because there are a number of famous patented and funky looking inks by Blackwood & Co..." @ Potomac Pontil. (dig photos there)
"BLACKWOOD & Co / PATENT / LONDON
Light olive green glass, height 2", dome shaped with offset neck, BIM with sheared lip, smooth base, item I#229, near mint condition, SOLD." From Reggie Lynch