What causes 'milk' spots on silver proofs??
Ed62
Posts: 857 ✭✭
. . . . . And can they be safely removed?
Ed
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Ed62
Posts: 857 ✭✭
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The milk spot comes usually post mint from what I hear. It's what I see as, "bad toning" caused by improper storing.
<< <i>It's likely there might be more than one cause for the spots, but generally they are caused by reaction of the silver with hydrochloric acid which remains when the planchets are insufficiently rinsed after a hydrochloric acid wash during manufacture. IIRC this acid washing step was added to the process in 1921 which partially explains why the 1921 Morgans and Peace dollars [among other silver coins] tone differently than earlier dated Morgans. Once visible to the eye, it is difficult or impossible to remove them without etching the coin's surface. It has been said that they can be seen using a halogen flashlight before they become visible to the eye and at that point they can still be removed with EZest. >>
Thank You for a logical and informed answer that has nothing to do with back alley heresay.
The name is LEE!
<< <i>
<< <i>It's likely there might be more than one cause for the spots, but generally they are caused by reaction of the silver with hydrochloric acid which remains when the planchets are insufficiently rinsed after a hydrochloric acid wash during manufacture. IIRC this acid washing step was added to the process in 1921 which partially explains why the 1921 Morgans and Peace dollars [among other silver coins] tone differently than earlier dated Morgans. Once visible to the eye, it is difficult or impossible to remove them without etching the coin's surface. It has been said that they can be seen using a halogen flashlight before they become visible to the eye and at that point they can still be removed with EZest. >>
Thank You for a logical and informed answer that has nothing to do with back alley heresay. >>
A few years back when the $50K reward [which I don't believe was ever claimed] for a means of removal was being offered by PCGS, I had an acquaintance analyze one badly spotted ASE removed from a NGC holder. We used a technique called ESCA [electron spectroscopy chemical analysis] or XPS x-ray photoelectron spectroscopy which is useful for the analysis of small amounts of materials on surfaces. The only element we found [other than silver] was chlorine/chloride.
The price of gold is set by faith, or lack of, in the currency it is priced in.
<< <i>our Host has a restoration service now.this year, , last year I sent five proof silver eagles back under the gaurantee .. they removed the spots, and they looked great.. >>
Interesting. I didn't realize that PCGS can now remove milk spots from coins.
Worry is the interest you pay on a debt you may not owe.
"Paper money eventually returns to its intrinsic value---zero."----Voltaire
"Everything you say should be true, but not everything true should be said."----Voltaire
<< <i>
<< <i>our Host has a restoration service now.this year, , last year I sent five proof silver eagles back under the gaurantee .. they removed the spots, and they looked great.. >>
Interesting. I didn't realize that PCGS can now remove milk spots from coins. >>
"Proof" Silver Eagles, have never been much of a problem.
The uncirculated versions are as the spotting cannot be removed.
The name is LEE!
<< <i>More specifically what is the likely cause of 'milk' spotting on 1870's - 1880's silver proofs - - - and can such spots be safely removed?? >>
Most likely the same thing that causes them now. I don't know if mint records from that era would show that an acid wash was used in the process. How common is the problem with those coins? If you can find someone doing ESCA that has a large enough sample chamber, it should be a non-destructive process. We had to cut an ASE into pieces in order to get it into the available sample holder. The sample is subject to very high vacuum [10 to the -7 torr] as I recall, then zapped with electrons. The gent did remark about how "dirty" the ASE surface was. There are commercial services that do ESCA, but I'd expect it will run about $200 per hour or more.
<< <i>Interesting, I had not heard that PCGS can now remove milk spots.... would like to see our host confirm this. (I have been away from the forum a lot this year, so may have missed it). Cheers, RickO >>
...good question ricko.........
<< <i>Does this apply to Franklin proof halves also ? >>
Applies to all silver coins from 1921 on.
<< <i>
<< <i>Does this apply to Franklin proof halves also ? >>
Applies to all silver coins from 1921 on. >>
So, what change was made at the mint in 1921 that started to cause milk spots on silver coins?
Worry is the interest you pay on a debt you may not owe.
"Paper money eventually returns to its intrinsic value---zero."----Voltaire
"Everything you say should be true, but not everything true should be said."----Voltaire
<< <i>
<< <i>
<< <i>Does this apply to Franklin proof halves also ? >>
Applies to all silver coins from 1921 on. >>
So, what change was made at the mint in 1921 that started to cause milk spots on silver coins? >>
Most likely the acid wash mentioned above.
In a nutshell he mentions that milk spots are most often found on silver proofs from 1958 to 1964 (I agree with this observation). Small spots may be removable but large spots were not removable with any known cleaning agent available at that time.
He also mentions that there was considerable debate on the cause (still is). The opinion of several mint employees that worked there at the time was that the spotting was due to residue from a cleaning solution that was used on the planchets prior to striking. Ivory soap was frequently used, but there were other materials that were experimented with. (I seem to recall that cream of tartar was mentioned in some other reading.)
So if the mint was experimenting with materials, we may never know what caused the worst milk spots. What I can say is that the problem is on intermittent coins. This suggests that the cause was also intermittent and could be related to improper control of normal process solutions or the experimental materials.
“In matters of style, swim with the current; in matters of principle, stand like a rock." - Thomas Jefferson
My digital cameo album 1950-64 Cameos - take a look!
<< <i>In Rick Tomaska's book - "Cameo and Brilliant Proof Coinage of the 1950 to 1970 Era", he discusses milk spots on page 26 & 27.
In a nutshell he mentions that milk spots are most often found on silver proofs from 1958 to 1964 (I agree with this observation). Small spots may be removable but large spots were not removable with any known cleaning agent available at that time.
He also mentions that there was considerable debate on the cause (still is). The opinion of several mint employees that worked there at the time was that the spotting was due to residue from a cleaning solution that was used on the planchets prior to striking. Ivory soap was frequently used, but there were other materials that were experimented with. (I seem to recall that cream of tartar was mentioned in some other reading.)
So if the mint was experimenting with materials, we may never know what caused the worst milk spots. What I can say is that the problem is on intermittent coins. This suggests that the cause was also intermittent and could be related to improper control of normal process solutions or the experimental materials. >>
Great book, glad it was referenced here or I was going to. good book!