1) How long does a batch (made up of dry stuff) normally last
(how can I tell when it is bad)?
G’day Carrie; Liver of sulphur when in the presence of water, is not
very stable. Indeed I would suggest that it would be of little use
after a day. It is composed of sulphides of potassium, but in the
presence of oxygen (air) and water it quickly oxidizes to potassium
sulphates, and the sulphur atom in sulphates is fairly well locked in
and unavailable for combination with metals like silver and copper to
produce black sulphides.
The suggestions above also apply to lime sulphur - calcium
polysulphide - which deteriorates quickly - and similarly - but is
the far cheaper and more readily available option for metalsmiths.
2) Is there any down side to re-heating it in the
microwave?....
There isn’t much point reheating; it is so cheap that one should make
up a solution that is sufficient for one’s immediate needs, and when
finished, throw away the remnant. It could be heated by microwaves
easily enough, but it might stink out your nice oven! Lime sulphur
liquid is so cheap that there is little to gain in trying to save a
diluted solution or squeeze the last drop of usefulness out of it.
One would dilute the liquid to around 10%, use clean, grease free
metals and use it warm - say below hand hot - though you wouldn’t need
to put your hand in it; that just gives an idea of the working
temperature which isn’t important anyway. The hotter it is the
shorter is the time it lasts though.
3) Is it safe to immerse stones briefly in it? I assume pearls
wouldn't be okay, likewise maybe opal, any others or should I steer
clear of all stones in the solution?
It seems to me that any stone based upon calcium or phosphate, or
softer than about Moh 6 would be unsuitable for putting in a sulphide
bath.
4) Is neutralizing the solution with baking soda all I need to
do to dispose of it safely? We are on a septic (I read the
discussion about that) and I do not have access at all to city
sewage (we are very rural). Any other considerations for disposal?
I too have lived in 2 (different) rural areas where sewage disposal
is the responsibility of the house owner. Yes, we had septic tanks -
which worked very well for at least 12 years in each place until
overtaken by sewage reticulation and disposal by the local council.
And yes, I disposed of sulphide discard in both. When one considers
that a whole variety of bacteria earn a living by breaking down
sulphur bearing compounds and converting them to sulphate, others
convert sulphate to elemental sulphur, and yet others start on the
sulphur - a regular jungle of fierce competition in the sewage lines!
Which is why modern sewage systems work. Agreed, many heavy metals
such as copper, arsenic cadmium, chromium, lead… will poison a
septic system, but not noticeably if the amounts are small. Anyway,
there exist bacteria that even tackle these when well diluted. As for
copper, many vertebrates use copper in their blood instead of iron.
One should also take into account that in sewage one might find every
possible compound that can exist, but there is so much of the stuff
that inclusion of a litre or so of substances bad for the bacteria,
form literally a drop in the ocean. It is only when huge amounts of
deleterious chemicals - chlorine, sulphite cyanide, heavy metals and
so on from industry enter a system that bad things happen.
However, having said all that, if you really want to be
environmentally squeaky clean, you could mix the discard with baking
soda solution until the fizzing stops, then pour it into sawdust
(rural areas have plenty available). Spread it out and let the sun
(if any!) dry it off. Bundle it in newspaper and dispose of it in the
usual way for solid rubbish. Or simply scatter it over the local
rubbish tip. Apartment dwellers might have to buy ‘kitty litter’. –
Cheers now, John Burgess; @John_Burgess2 of Mapua Nelson NZ