Sciencemadness Discussion Board

sulfur and tarnishing

grace - 12-8-2011 at 08:46

I have an 8 torch beadmaking studio. The torches are surface mix propane/oxygen. My question to anyone who has any ideas on how to neutralize the effects of the sulfur is this: Since opening the studio, the sterling silver jewellery on display tarnishes within days - and tarnishes a lot. My best guess here is the effects of the added sulfur in the air from the propane used by the torches accelerates the tarnishing process. This same situation is occurring in a glass blowing studio in the city as well. Same idea – propane is the gas they also are using.

Any ideas out there for what I can do besides changing to another fuel or bagging the silver in order to slow down the tarnish process?
Thanks so much! /g

Fleaker - 12-8-2011 at 08:50

You can bake the silver in an oven and the silver sulfide (Ag2S) will turn into silver oxide (Ag2O) which will then decompose to Ag and oxygen.

hissingnoise - 12-8-2011 at 09:07

Humidity, temperature, air circulation and bright light, especially sunlight will increase the rate of Ag<sub>2</sub>S formation and needless to say tarnished silver should be cleaned when the discolouration first appears!
It's a real problem because the causes of pollution are many and varied . . .

Some kind of airtight enclosures, possibly?

hissingnoise - 12-8-2011 at 11:03

Grace, ethanethiol is the usual odourant in fuel gasses - propane without this compound should lessen your tarnish problem!

grace - 12-8-2011 at 11:13

Thanks for the quick responses.

Baking it is out of the question as it is finished jewellery. I do have some containers, but some of the jewellery needs to be out in the open.

I don't believe I can have the propane without the additive - even though that would no doubt alleviate my problem. Any other ideas?

fledarmus - 12-8-2011 at 12:21

Unfortunately, there is no way around the sulfur in the propane, and it will tarnish your silver. You can minimize the effects by doing all of your soldering in an efficient fume hood. You might also try spraying or dipping your jewelry in one of the "instant detailing" solutions used by car buffs - they will leave a thin film of wax that will help delay the tarnishing. The film can be removed by cleaning with an ammonia-containing cleaning solution when you sell the pieces.

Some of the suggestions here might help you, especially the 3M Anti-tarnish strips. Boxing the pieces at night in a box that has these strips might also help. The activated charcoal in the strips absorbs the sulfur compounds which would otherwise be floating around in the air.

hissingnoise - 12-8-2011 at 13:06

Your supplier should know if ethanethiol-free propane is available for special purposes.
And of course, the actual quantity of odourant in these gasses is quite small.
The other thing is that ethanethiol can be condensed by a cold-trap @ <0°C (fitted in-line) as its b.p. is ~38°C, but fitting such a cold-trap should be carried out by a competent technician.
It really depends on how far you're prepared to go . . .
And air-borne sulphur compounds will still be a problem!


[This] From Silver-care and Tarnish Removal . . .

All silver objects should be kept clean and free of dust and surface grime.

The formation of tarnish inside display cases can be minimized by using desiccated silica gel to keep the relative humidity (RH) low, and activated charcoal or a suitable commercial product to remove tarnishing gases.

Tarnish need not be removed before storage. It is better to remove tarnish from silver only when necessary, e.g. for display purposes. Whether or not silver needs to be stored with a bright and shiny finish will depend on a variety of factors that must be considered for each collection.

Tarnishing can be minimized during storage by placing individual silver objects inside polyethylene bags and then sealing the bags using tape, heat sealing, or a self-sealing bag. It is always good practice to wrap or support each piece of silver with acid-free tissue paper (“non-buffered” or “unbuffered” which is sulphur-free and of archival quality) to buffer changes in RH and to prevent transfer of harmful materials from the storage environment to the silver. Additional protection against tarnishing can be achieved by placing small containers of desiccated silica gel and activated charcoal inside the bag. Alternatively, the silver may be wrapped in a tarnish-inhibiting cloth before being placed in the polyethylene bag. Tarnish-inhibiting cloths that are embedded with tiny silver particles (e.g. Pacific Silvercloth) are particularly effective because any tarnishing gases that are present will react with the silver in the cloth before they can reach the object inside. Because of the processing method used to introduce the silver particles, this type of cloth is available only in dark brown. Tarnish-inhibiting cloths that contain metal salts are also available, but these are less effective than those that contain silver particles.

Lacquering or waxing is not recommended for silver because of the difficulties in obtaining an even coating. If the coating has not been applied well, it may be uneven or have streaks and small holes. If this is the case, the end result of any retarnishing may be worse than if no coating had been applied at all. However, in an open display where a coating is deemed to be necessary, microcrystalline wax or lacquers such as the acrylic Incralac or the nitrocellulose Agateen #27 are suitable.

grace - 12-8-2011 at 13:10

Quote: Originally posted by fledarmus  
Unfortunately, there is no way around the sulfur in the propane, and it will tarnish your silver. You can minimize the effects by doing all of your soldering in an efficient fume hood. You might also try spraying or dipping your jewelry in one of the "instant detailing" solutions used by car buffs - they will leave a thin film of wax that will help delay the tarnishing. The film can be removed by cleaning with an ammonia-containing cleaning solution when you sell the pieces.

Some of the suggestions here might help you, especially the 3M Anti-tarnish strips. Boxing the pieces at night in a box that has these strips might also help. The activated charcoal in the strips absorbs the sulfur compounds which would otherwise be floating around in the air.


yes, I did kinda figure that. But I also wondered if small containers of activated charcoal might slow down the process or absorb some of the sulfur. Any thoughts about that?

redox - 12-8-2011 at 13:41

Feast your eyes!

http://www.youtube.com/watch?v=vGCx9HZwYBo

This is a great video by our own member Nurdrage depicting how to restore silver.

Endimion17 - 13-8-2011 at 05:39

Aluminum foil and salt solution is one of the oldest known, noninvasive modern (modern as aluminum is) methods, and it's probably the best. It's been done like that for the whole 20th century, if one had aluminum.

But he needs a way to prevent the tarnishing. Not much can be done. I don't recommend cold traps, as an accident can happen. If the gas leaks from a cold trap, and chances are it will, he might not sense the smell, and a buildup could occur, leading to an explosion.
Cold traps are ok for experiments, but for running equipment on daily basis, no.

Odorant-free gas should be available, but requires caution. I'd just bag as much silver I can and resort to aluminum foil method.

Mr. Wizard - 13-8-2011 at 07:10

In the US, ethyl mercapitan is the usual gas odorant. It has an intense smell, and a leaking bottle of it can be smelled for miles, even on a breezy day.

Gas leaks underground will often discolor wiring and blacken copper wires, as the gas follows the conduits and tubing. The sulfur in the mercapitan reacting with the copper wire and with the coloring agents in the PVC wire insulation.

Copper wire and copper wool was used in the oil country of Texas and Oklahoma to remove sulfur from 'drip gas'. Drip gas ( raw unprocessed gasoline) is the longer chain alkanes that are carried along with natural gas out of a gas well. They are removed to prevent liquids from forming in the natural gas lines. Friends who used the gasoline in their cars would tell of running the gasoline through a container filled with clean copper wire, which would react with the sulfur to form a black material. This process takes some time and is not an immediate reaction.Failure to remove the sulfur would often result in engine bearing failure, as many engine bearings contain some copper.

It might be possible to remove any sulfur compounds by passing the fuel through a solution of a soluble copper compound,such as copper sulfate, or a mesh of copper wire. An easy method would be to bubble the gas fuel at low pressure though a plastic container filled with a solution of copper sulfate. If the solution starts getting a dark precipitate of copper sulfide forming in the bottom or sides, you know it's working.

There are 'other' sources of sulfides in the air. It's well known that boiling cabbage can give off enough sulfur to tarnish silver. As a child , the combination of cigarettes, and cabbage in our house could blacken silver in days. Flatulence is also another source of sulfur. A diet of broccoli, eggs, beans, or other known gas producers may cause a problem. Check to make sure your sewer vent pipes are in order. I have worked in older buildings where the seals around toilets were not exactly gas tight, or a priority. The tarnish may not be from one source, and it may take a combination of steps, and increased ventilation to reduce sulfides in the air.

Another problem may be leaking natural gas into your work place. I would expect the sulfur odorants to be converted to sulfur dioxide after passing through a flame. This shouldn't darken silver. Leaking gas containing unburned odorants will darken silver. When you come in to work in the morning, does the workplace have that funky smell? I can speculate with 8 torches going you have a lot of gas piping around, and a lot of flexible tubing with fittings. Normal wear and tear on hoses will cause leaks, and people will get used to small amounts of leakage at fittings, valves, and connections.

I'm sure your local gas company that supplies your propane has or can recommend someone to come over and inspect your gas distribution system. It may also keep you from having a big safety problem.

You might also check to make sure you have enough air exchange in your workplace.

AJKOER - 13-8-2011 at 08:42

If your cleaning method involves Aluminum, I would suggest pre-soaking the Al in vinegar for several hours. My reference was a website that address making coatings and hardening Al foil to be more resistance. The manufacturer lamented the power of vinegar to bypass many of their defenses. I perform this pre-soaking and noticed little of a reaction, but subsequently noted an increase ability of NH4OH to dissolve the Al2O3, and speed up the hydrolysis of Al by H2O (that is, the Al foil appears to dissolve more rapidly in NH4OH with pre-soaking with vinegar of the Al). So, with any experiment involving Al, try to pre-soak the Al and see if things proceed more rapidly.

Mr. Wizard - 13-8-2011 at 14:33

I think he is trying to prevent the tarnishing, rather than looking for an easy way to remove it. If he has a shop full of silver items he doesn't want to have to process his entire inventory each week.:)

AJKOER - 13-8-2011 at 18:48

One idea that presents itself is, as before, hang or use as shelf linings, activate Al foil (that is, pre-soaking for a few hours in vinegar). Now, I would guess that any sulfur in the air would first react with the activated Al foil before the Silver. A similar concept, clean copper pennies and spread them around and use them to capture some of the sulfur. Downside, foil will turn yellow and will have to be replaced. The pennies will have to be cleaned as well. Silver may still require cleaning.

More reactive approach, get a fish tank with pretty rocks and an oversize air pump (no fish). Add a sulfur scrubber to the tank like a solution of NaOH for example. If one used the highly Sulfur sensitive Lead Acetate (prepared by adding Lead to a solution of H2O2 and vinegar), for example, the outflow air would have to be run into a second tank to remove the acetate smell. Basically, you have an air scrubber system disguised as a fish tank.

Another more direct approach would be to place cleaned Silver jewelry in a large see-through plastic display boxes (or, even open top boxes). Use a CO2 fire extinguisher to fill the containers with CO2 (Caution: be aware of a suffocation hazard). Periodically refill. The heavy CO2 should shield the jewelry from air and sulfur. The approach is inexpensive, odorless and easily obtained and applied (your CO2 fire extinguisher).

Combining the air scrubber and the CO2 approach should be effective in reducing tarnishing.