There are several Sheffield makers with the initials IW.  This means that we cannot be absolutely sure when we see the maker’s mark IW.  The makers are:

Joseph Wilson, October 4^th 1773

Jonathan Watkinson, October 3^rd 1776

John Wright, October 12^th 1789

John Wilkinson, March 18^th 1790

John Watson, September 24^th 1795

This particular pair of tongs is dated 1799 and is fairly plain with a light feather edge.  given the date, they are likely to be either John Watson or John Wilkinson.