I wrote and tried to post this before Trev posted anything. But I am adding a few sentences here: I invite people to compare the engraving, on the monteith bowl avaiable on line. As for the mark, Daniel Henchman had a two letter mark whose use predates the dates given for this spoon.
A Google search now turns up the back of the Dolphin end of the spoon. It has what appears to be a shallow indention. Thus explaining why someone might think it is a marrow spoon.
I guess it won’t hurt to explain that marrow spoons are basically a marrow scoop with one end being a spoon. In other words it is a normal spoon with a long narrow channel or grove going the length of the handle. The British ones I have had were mostly Queen Anne period or somewhat later. They were more of less replaced by scoops in the mid-18th c. As usual there are always exceptions.
Both forms are exceedingly rare in American silver (Hurd made one). I was lucky enough to have one of each style, and have only seen a few others.
Why is it fluted? Fluting is an odd thing to find on spoons.
Generally fluting is a method of increasing the strength of sheet metal, etc. Think of corrugated roofing, cardboard etc.
On spoons it makes less sense. Mostly in the 19th century it is seen on fruit spoons. Where strength is needed and the eaten object is in a chunk form. It is hard to eat something like porridge from a fluted spoon, you can’t lick them clean. Also fluting makes it difficult to scrape the bottom of the bowl, probably why the French didn’t use it much. So in the 18th c. what kind of things had fluted bowls. Salt spoons, caddy spoons, and ladles. I always presumed it was because a fluted bowl, might make pouring easier or prettier, or was just a replica of a shell bowl, which was a naturalistic sort of embellishment. Certainly it made no difference that you could not scrape a salt dish or tea caddy bottom. I am not so sure why they were so popular on large ladles, unless it was just that they are so pretty. In any case fluting tends to be used mostly on serving pieces.
As far as 18th century American spoons with fluted bowls, I couldn’t think examples by even a handful of makers. And they are all tea spoons. If a teaspoon is only used for tea then fluting causes no inconvenience and is very pretty; Paul Revere made a few.
I don’t know what this spoon is, but at 20 cm. it is no tea spoon.
It turns out the spoon is not marked, so the “attribution” I presume must primarily be dependent on the engraving, and the known Monteith bowl. It also depends on there being only one “John Wentworth, Esq.” having a friend named “Thomas Smith”. In my opinion extraordinary claims demand extraordinary proofs.