Old method of gilding, how?

A friend of mine who is a restorer of old weapons is looking for an old method of gilding steel.
Not the fire gilding or the inlay or overlay but as he discribes it must be a method of preparing the steel with nitric acid or something like that and then put very thin sheets of gold on it without a layer of glue between this.
Does anybody know an old method that comes close to this describtion?

http://www.restauratorenverenigingnoord.nl/restauratoren/imgs/prummel/Der_Experte.pdf

http://www.restauratorenverenigingnoord.nl/restauratoren/prummel.html

not sure if it works on steel. but this is QUITE DANGEROUS !!! TO DO. MUST BE DONE OUTDOORS. YOU MUST BE UPWIND OF THE ITEM BEING WORKED ON!!!!
disolve some gold in mercury. apply mercury/gold mix to the part. gently heat the part with a small plumbers' torch. when the mercury boils off, you have a gilded part.
if the fumes from this procedure ARE BREATHED IN, YOU HAVE POISONED YOURSELF !!! EVER HEAR OF "THE MAD HATTER" ? IN DAYS GONE BY, MERCURY WAS USED TO HELP SHAPE FELT INTO HATS !
one could also brush plate such a part, far less danger involved doing it this way. enough gold solution to do some small parts would run about 50 bucks- us dollars +shipping
caswell plating.com you don't have to purchase the expensive dc power supply. it can be done with a common wall wart . you probably already have the goodies to do this. a couple alligator clips, some light guage wire. THIS BRUSH PLATING technique does not lay down a very thick layer of gold. should be done only on items not being handled very much.