I have bought letter sealing wax in the past (I used it to stick clarinet pads back in their seats after they came loose after marching in the inevitable rain storm). The stuff is in stick form, about 6 inches long, by about 1/2 by 1/4 ". All that is required to seal a letter is a small blob about the size of a quarter, and only that thick also. A secondary heat source (a candle) could be used to melt a small portion off the end of the stick, to drop on to the flap and body of the letter. After which, some kind of stamp is pressed into the still hot wax, to press it into place, and to add a identification mark, if needed.
I can't imagine that a constantly molten source of wax, which would be necessary to use a ladle like the ones dicussed, would be practicle for any where other than a large office mailing department that did nothing but mail letters all day.
I cast my vote for canning jar sealing.
Fred