I use to add some alcohol to avoid foaming, if not the rxn is not elegant and I guess less reproductible.
How much Zn, please ?
Rhodium, I've tried tha NH3 basification, but it didn't worked, or at least it was not the oil floating on the top like with NaOH. It was a small test, 50 % basified with NaOH and 50 % basified with NH3, and the oil appeared with NaOH and not with NH3, I didn't make the work up with this 1 gram escale, it's too much for me.