I am a blacksmith working at a local museum. I came across an old pair  of tongs in their collection. The surface shows a little rust and lots of grain , typical of old wrought iron. It's clearly hand forged and massive. 

It's about 24 inches long overall. The bits are (each) one and a quarter inches square and about five inches long.  It's clearly designed for holding flat stock .

Can anyone suggest what these tongs were used for? 

I heated the jaws to a dull red heat and clamped them on to the spine of a scrap knife blade and in a short time I could see the tempering colors flow from the spine to to the cutting edge. It was easy to arrest the action without over heating the cutting edge. 

Has anyone seen similar tongs and/or confirm their usage? 

 

no photos? this is a "what kind of car to I have, it has 4 wheels" type of thing

1 hour ago, dickb said:

Has anyone seen similar tongs and/or confirm their usage

I have seen tongs that appear to match your description and they were described to be used as tempering tongs, just as you successfully used them.  Of course it could just as easily be a case of a similar tool working for more than one application (as Steve indicates), but I think you have more likely than not correctly figured these out.

A photo would be nice though, as the only ones I've seen to date were pretty clearly a modern set cobbled together.

Brazing tongs for things like bandsaw blades is my guess; depending on the width of the jaw gap.  I have a set and they close on less than 1/8" stock and are excessively massive.