I have yet to see toning on low grade coins. I only see toning on MS coins and sometimes AU coins. Rarely XF. Coins VF and lower I have never seen with toning. I have seen them tarnished but not toned. Is there a reason for this? I thought maybe because the toning has been rubbed off but I have junk silver that has not seen circulation for 100 years, so that cant be it.
Many factors play into this, such as how the coins are stored, but yes even junk silver can tone. When there's a presence of hydrogen sulfide, or most any sulfur containing material, in any material silver comes in contact with, it will tarnish.
One of the reasons you will see so many more colorfully toned uncirculated coins is due to the luster. The toning or tarnish has a much rougher surface to adhere to, in combination with air flow over the surfaces. Think of it this way. The luster gives the surface a pattern similar to this /\/\/\/\/\/\ When the luster is removed due to circulation, it flattens. --------- As BU said, circulated and low grade coins will still tone. Although more times than not, with undesirable effects. The colors will usually be much more muted since it doesn't have the added benefit of the luster to make them pop. Here are a few circulated examples where the toning did generate some decent color. When the condition and luster are better, the colors just look better. Even same or similar colors are much more eye appealing as the grade/luster goes up.
Is it possible that you're wrong on this? I mean, I think a lot of it has to do with orientation, as opposed to simply adherence. If you imagine a piece of suede, rubbing in one direction yields a darker color than rubbing in the other. Similarly, opals will show play of color in certain orientations better than others. I think toning oxidation might work in a similar way to how the opals work. The angles created by the formation of Ag2-S on the surfaces of the coins diffract light at different directions. When you have the ridges from striation /\/\/\ , your eye receives light at different directions/wavelengths/velocities/whatnot, which results in different colors. When those ridges change /U\|\|\/|/|U--U\/ , light reaches your eye at less defined angles, which muddles the colors together. Even if the ridges were the same "height," you would still end up with less defined (darker saturated) colors. At least, that's what I think is happening. I might be wrong. It's happened before.
The first thing you need to understand is where the colors in toning come from. Silver sulfide itself is actually black in color, so where do the colors come from? It comes from the light passing through the thin layer of silver sulfide, reflecting off the surface of the coin, and passing back through the layer again. The light waves as they pass through the layer interfere with each other strengthening some wavelengths and cancelling out others. What wavelengths get reinforced determines what color we see. And the thing that determines that color is how thick the layer is. It's called thin film interference. Now what determines how thick that layer is? Two major things are distance from the source of the toning, and contaminants on the surface. think of the bullseye toning you get from an album. The lighter colors are toward the center farther from the edge of the holes and closer to the edge you get the darker colors. Layers of oils, either from machines or skin oils results in slow growth of the silver sulfide layer. Clean areas grow the layer faster. On an uncirculated coin the surfaces tend to, but don't always, have roughly the same thickness layer of contaminants across the coin so toning is relatively even. But as the coin wears it collects skin oils and DIRT. All this stuff rapidly results in thick contaminated layers that do not show colors. Now over time that coin can still continue growing a silver sulfide layer getting thicker and thicker until you have a black tarnished coin, but you don't get color. But the wear the coin is not the reason you don't get color. If you take a worn coin and strip the surfaces back down to clean bare silver it may look dull and dead, but over time as the silver starts to react again it IS possible for colors to appear. The coin still won't look good, but it can have color.
You're both saying the same thing. Toning is quite simple, it is due to the refraction and reflection of light as it passes through the chemical compounds on the surface of a coin. As to your question - does junk silver tone ? Yes it does. And toning and tarnish are just different words for the exact same thing. You say that you have never seen circulated coins tone. Well, they do, but they do not tone as easily or as quickly as unc coins because of the differences between circ coins and unc coins. Just because you have never seen it, that does not mean it does not exist. Toned, well circulated coins do exist, they just exist in small numbers because of those differences. And the differences have been explained.
