I have a collection of Swiss silver spoons, starting around 1750. Spoons from this type are common in my collection, they usually date from 1800, take or give a few years. However, I have not many spoons from outside Switzerland, so I have little experience if this type is common in Europe or rather specific Swiss. I leave this assessment to other forum members.
If the spoon HAS TO BE Swiss, it is difficult finding a match. I could not find a match in Weltliches Silber II, which is very complete on flatware from this period, nor in Weltliches Silber 1, which usually deals with older silver.
I am not aware of a city mark starting with I..., so I assume this is the maker. Then the city mark is the Z shaped mark. Z fits for Zurich, however, they changed from the Z to the coat of arms in 1779. And the spoon does not look older than 1779. And the Z in the Zurich city mark looks different, and there is no maker mark match starting with an I for Zurich short before 1779, and...
I do not think the Z..ish mark is really a Z, but what it is, I do not know. Maybe some other memebers have a good idea.
Kind regards, Jörg