You’re looking for products which combine relative safety with
effectiveness. It’s almost a contradiction in terms, because with
many substances in life, the more effective it is at its job, the
more hazardous it seems to be. The milder, safer alternatives, if
they do do the job, will usually do the job more slowly (talking of
pickle here, not flux), and the quicker-acting ones are generally the
more hazardous ones. However, as James Binnion pointed out, while
citric acid is a safe substance to begin with, it is rendered toxic
as soon as it has been used a a pickle, due to the dissolved copper.
Perhaps the best approach might be to take the middle ground with
something like pickle, and stick with the sodium bisulfate
alternatives (pH Down, pH Minus, Sparex, or plain sodium bisulfate
from lab supply which is what I use). It does the job really well
and quickly, but does not cause nasty burns if splashed onto the
skin, as something like sulfuric acid would do - obviously you’d wash
it off immediately in the event of a splash in any case.
Make sure it’s in a decent, safe container, and that it’s well out
of reach of children and pets, and follow any safety advice that goes
along with whatever chemical you choose.
Flux seems to be a more complicated issue, and it seems to be a
personal preference type of thing. You find a soldering regime which
works for you, but it may not work for someone else - and flux falls
If you’re soldering silver, you’ll want a firecoat as well as a
soldering flux. The firecoat protects the whole piece against
firestain while soldering, whilst the soldering flux, used at the
joint, keeps the oxygen away from the joint and the metal in that
area clean so that solder will flow into the joint. Some folks will
use two different fluxes for those two needs, whilst others find that
one flux will do both jobs. Personally, I use Prips flux and mix it
myself (the recipe is in the Orchid archives). Some folks find it to
be a good firecoat but not a good soldering flux - I find it works
fine for both jobs.
With regard to safety, some are obviously more benign than others,
but you should always take precautions when soldering to avoid
breathing in any harmful fumes. Prips seems to be a pretty safe but
effective flux as far as I can tell. I’ll be interested to hear what
others have to say.