I imagine there are quite a few variables to scuttle temperature: thickness of the walls, size of the water reservoir, size of the opening, etc. I ignored all of these as I have but one scuttle - a big Robert Becker.
I filled the scuttle from the tap (114 degrees) and left the cover off. In 10 minutes the temperature was down to 104.
Leaving the cover on, in 10 minutes the temperature was down to 111 degrees.
I'm not sure how significant that difference is to your lather. It should be noted that the Becker scuttles have a small opening. I would imagine that a scuttle with a much larger opening would have a greater heat loss.
I filled the scuttle from the tap (114 degrees) and left the cover off. In 10 minutes the temperature was down to 104.
Leaving the cover on, in 10 minutes the temperature was down to 111 degrees.
I'm not sure how significant that difference is to your lather. It should be noted that the Becker scuttles have a small opening. I would imagine that a scuttle with a much larger opening would have a greater heat loss.