Featured What You Need to Know About: The Science of Toning

A silly but yet serious question: Does this statement:

"Hydrogen sulfide in large concentrations is very toxic and flammable, but small doses are almost always present in the environment. "

mean that you could get sick or even die if you licked toned coins? Obviously you'd probably have to be doing that a lot, but I am wondering if it is even possible.

I'm not a fan of toned coins, but I am a fan of science.

 

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Hydrogen sulfide is readily produced by the action of an acid on "-sulfide". Many foods such as onions, garlic, beer,irradiated meat...contains sulfides that could interact with the hydrochloric acid in your stomach to produce hydrogen sulfide, but the amount to be consumed would be extremely large. But ....

Our intestinal tract contains bacteria which can breakdown passing food residue and produce hydrogen sulfide from normal sulfur containing amino acids. This gas can pass through the digestive tract and emit as flatulence, accounting for some of the odor and flammability of anal emitted gas. This is a much larger amount of gas than by ingested means.

As far as I know, no one has died from flatulence. Perhaps people around them think they will.

Artists know there are some zinc sulfide containing paints one should not eat as they can also produce much larger amounts of H2S.

Jim

 

Astronauts are particularly at risk, so generally the food as well as the design of space toilets try to prevent any buildup of hydrogen sulfide, although the alarm sensors have triggered before with certain astronauts. The bacteria actually seem to grow better in null gravity.

The Chinese use a "pump and store " method
http://english.peopledaily.com.cn/200510/14/eng20051014_214307.html

Jim

 

The Apollo recovery teams had special SCUBA gear issued because of such concerns. (look it up)
And they were just going to open the hatch.

 

Which of your nice armaments did you use ??

Jim
​

 

Brilliant post! I really think you should submit it to a publication like the Numismatist.

Now I'm concerned that all my coins will get AT if I eat too many burritos.

 

Now all we need is to program the nanobots to arrange the silver sulfide into the patterns and colors we want!

 

best technical post ever

I agree, this could be an excellent article for the Numismatist.

As far as surface "oxidation", some metal oxides (e.g., aluminum) form a passivating surface stopping subsequent metal surface degradation. Other metal oxides (e.g., iron) seem to act more a thoroughfare than a barrier. Two examples are the aluminum coating on the mirror of the 200" Mt. Palomar telescope and iron rust.

 

Wonderful article: that's the sort of thing that makes me save a magazine when it appears in print.

Being me, I of course still have a question. If dipping solutions don't affect the underlying silver, how do they damage the flow lines?

I remember from one of Doug's many informative posts that the timing of a dip is critical. Is it that a brief dip doesn't materially affect the bulk of the silver, but still has time to dissolve the exposed and stressed metal of a flow line?

If there were a chemical that somehow dissolved or dissociated silver sulfide without affecting silver (there must not be or people would be using it) would it leave luster intact? Or would the sulfide attack already have ruined it?

 

Great question sponge.

Dipping to remove toning affects luster because the toning affects luster. The surface of the coin is where the flowlines are which produce luster - it is also the top layers of a coin where the silver sulfide forms. It is the top layer of silver which reacts with the sulfer to form silver sulfide (some of the silver in the coin must react with the sulfer - its not just a film which is deposited). When you then remove the toning by dipping, you are removing the top surface of the coin - which is exactly the same silver which held the flowlines which produced luster.

Dipping removes a measurable amount of silver, and damages the luster. It is primarily for this reason that some argue toning is damage.

For more information on luster, read my article which I linked in one of my posts in this thread.

 

removing mass

Originally Posted by physics-fan3.14

(much wonderful stuff snipped)

When a toned coin is dipped, it is the thin film that is removed. Using a precise enough scale, a coin can be weighed and then dipped. A perceptible amount of silver (or rather, silver sulfide – most solutions do not affect the underlying silver) is removed in the process.

my guess is that you would be removing less that one milligram by dipping. Most inexpensive scales don't have that kind of resolution.. Another point to consider is that it is easier to strip off an atom residing on a sharp point than one in the middle of a planar surface. I believe that is one reason why luster (the diffusion of light off of microstructural flow lines) goes when you overdip.

 

Weimar White's experiments concluded that the toning was on the order of a couple hundred micrograms. Inexpensive scales certainly don't have that resolution, no, but that amount is easy to measure on a high quality scale.

 

For those who haven't seen that post, I recommend it highly.

 

Here's a link to a thread by Sunnywood on the CU forum about thin film interference and toning progresssion, which I think complements this one nicely: http://forums.collectors.com/messageview.cfm?catid=26&threadid=708296

 

Excellent post and thank you for sharing your knowledge !!

 

One more question, while I have a knowledgeable and helpful person on the line.

Why is there a detectable difference between natural and artificial toning? At first thought, all optically thin films of silver sulfide seem like they should be alike.

 

Well, for starters, many AT jobs use different chemicals, so its not silver sulfide you're seeing. That being said, a thin film will behave like a thin film optically no matter the substance.

The difference comes in how the film comes to be on the surface. As a coin sits in an album, or wherever, the flow of air and moisture, and the proximity and location of the source of sulfur, all affect how the toning appears. There is a certain look album toned coins get - and only they will naturally get that look. An AT job will not perfectly duplicate those same conditions, so the "toning" will look different.