Boiling water in dewars takes some time and it will be substantially inconclusive: if you will find a lot of foam, some people here will say that you did not use the same water, glass , salt, and so on used by F&P in 1992.
In the meanwhile, could you please tell us your opinion about the presence of foam in the cells as shown in the two available lab videos (1-2) of the "1992 boil off" experiment?
Is the interpretation given by Robert Horst (3) correct for you?
I will make foam. Lots of foam.
And then I will make the foam crust incandesce, because I know I can do it, because I already did do it 40 years ago.