This tool at Smith’s Tavern was supposedly used specifically for milk. This metal ladle has a somewhat long handle with a large bowl at its end.
As milk is heated, the water in its structure starts evaporating from the surface. This concentrates the remaining fat and proteins into a thicker layer at the top of the pot. This layer eventually becomes so thick that water vapor rising through the milk can’t break through very easily and gets trapped. So it can boil over. So a metal ladle was put into the pot as it is heating. The ladle breaks the surface tension and allows the steam to escape without erupting.