Are these polish lines?

Ok then riddle me this: - If die polish was/has been done the same way for decades, then why dont polished coins acrossed all series look the same?? IF what you say is true, then why dont we see multiple examples of circular parallel lines on thousands of different coins???? Fact is, i dont think ive ever seen a single example with those characteristics

 

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Great question. Unfortunately, I'll bet no one here was ever at the Mint when a clashed die was removed from the press and sent to be fixed. Die polishing was probably similar through the years and only changed as more modern tools were developed. One FACT that can be demonstrated/proved by looking at the coins is that early 20th Century commemoratives are often found with circular die polish and business strike coins usually have back and forth lines. Therefore, authenticators I've spoken with believe at least two different people/methods were used to work on the dies for each type of coin of over certain time periods.

 

I can help a little.
I have a group of 17 1959 cents that show 4 different dies with at least two coins with matching die polish lines on the obverse. I haven't studied the reverse yet.

Die 4


Die 3



Die 2







Die 1

 

We make a lot of polished cross sections of all kinds of metals and materials at my lab when doing failure analyses. We use a process much like that which GDJMSP noted (i.e. flat polishing wheels covered with various pads of descending grit size down to nanosized alumina, rotating 90deg after each step to remove the last steps polish lines). This puts a mirror finish on the polished surface. But once that polish is complete we are very careful not to touch or wipe anything on that surface because it will create scratches. We spray the polished surface off with water and blow it off with air and that is it. Even the tiniest speck of sand (which all dust has in it) on a wiping cloth will scratch it like crazy and ruin an hours worth of work.
I imagine the guys in the mint don't have to time to polish the dies to the same level we do which is likely why you see so many scratched up dies.

 

The examples that robec just posted look to me like someone polished by hand the rougher grit stage of their polishing protocol. By hand I mean they held the die with their hand and and spun in around randomly (often in a figure 8), face down, onto the polished pad (likely with 9um diamond or larger) instead of holding it onto a polishing wheel that was spinning uniformly and creating parallel lines. The Die 1 pictures look to me as if an attempt was made at polishing out the rough lines, which created the smoother areas, but they didn't spend the needed about of time to get rid of all the lines. When polishing a surface it is very important to hold the sample (die in this case) very flat. Otherwise the edges wear down a bit more and the final polish will not touch them, leaving the larger polish marks around the edge of the flat area as we see in die 1.

 

I must respect your opinion but until I see it.... Just because we can see a micro hairline scratch on a polished surface such as a die, does not mean it will reproduce as a raised line.

Now, let's take a proof SE. Take a greasy rag with some grit and rub the coin. We will be left with a hairlined proof surface. Based on over 45 years of examining the surface of all types of coins from all ages using a high power stereo microscope:

1. Die steel is harder than any of our usual coin alloys. You are going to need to put a decent scratch into it for it to reproduce!

2. The type of minute hairlines (into the surface of the Proof SE and used to illustrate what would happen to a steel die) WILL NOT PRODUCE any effects that are visible RAISED polish lines on a struck coin at magnifications less than 40X. Therefore, it is my contention that the typical polish we see on coins in this thread were caused by a much coarser type of polishing.

3. While hairlines are a type of micro scratch, NOTHING I have ever seen (using high power magnification) imparted to a coin's surface (raised) from a die comes close to having any resemblance or characteristic of a hairline caused in the quote above by something like a tiny piece of grit. Raised lines on a coin come in degrees of intensity. A hairline is not a scratch. A scratch is not a gouge or tool mark.

 

Insider, your point is a good one. The scratches that we see in the lab, and are worried about, may not be enough, if on a die, to show up on a coin reproduced from it. This I have no experience with. I just want to confirm that scratches can be caused by simply wiping a polished surface with a cloth or paper towel. But they would not be as abundant as what we are seeing here.
I think the lines we are talking about that can be seen on the flat areas of coins, like shown in robec's pictures, are from incomplete (or should I say imperfect) polishing of the die. The final polishing steps where either not done or done too quickly, IMO.

 

GDJMSP, I understand and agree with what you are saying but I have one questions. How do you know that everyone polishing die for the second time (after it has become damaged or worn) uses a polishing wheel? Isn't it possible that some without access to a polishing wheel might place a polishing pad of whatever grit or diamond compound, flat on a table and rub the die face down on the pad in a figure 8 for a few minutes? And now a days most of the polishing wheels have an auto head assembly that rotates the sample as the wheel spins below it. Both of these methods produce more random polish marks than the traditional hold it flat on a spinning wheel method.
I imagine that the first polishing of a new die has a strict SOP that dictates a proper polishing procedure that works such that we don't see any lines. But the second polishing seems more of a trouble shooting step that may allow the operator a bit of discretion on how to get the task done in as short a time frame as needed. Maybe you or Insider have a better understanding of Mint protocol.

 

Dang, this subject is like a Phoenix that cannot be put to rest. Most will agree with one part of Doug's post - dealing with fresh dies. To the best of my knowledge, the rest of the poster's opinion has only one proponent - himself.

@GDJMSP Thanks for the photos of dies that I will use to refute your ideas about die polish on coins. My reply, plus additional photo evidence will take several hours that I cannot spare at the moment. I look forward to presenting a dissenting opinion some time next week - much of which has already been posted in past threads without photos of actual dies.

 

FWIW - if you used a 1000X loupe, you might see them well. That stuff is so fine, purposely, that you cannot see it. The exception occurs when the wheel becomes scratched or something breaks loose.

 

I propose we designate a new category of Mint die treatment, called Die Abrading, to explain the abundant examples of coins showing crisscross die polishing lines appearing in this thread.

 

You guys over-think things too much. Trying to figure out how a machinist cleaned a tool is a mute argument. The machinist probably used whatever was at hand that got the job done to a satisfactory level as quickly as possible. .. you'd be amazed at how many problems in a machine shop can be solved with a hammer and a brass bar!

 

You know what...I think I'll just leave this "Phoenix" alone. Collectors, dealers, numismatists, authenticators, mint employees, researchers, error collectors, VAM enthusiasts, ect. (did I forget anyone?) can call the raised lines we find on coins whatever they wish. Whether resulting from mechanical polishing, hand work, scratch damage, or whatever - as @SuperDave posted: all scratches into the die - intended or not/microscopic or not - fall under the term ABRASION.

 

Doug, So you're saying all those curved and crisscrossed lines on those Lincolns I posted earlier in the thread are due to sanding and not polishing.

 

That's entirely fair. There's a huge difference between the initial basnining of a die (@Electron John, keep in mind that dies are generally not flat, but concave, for quality-of-strike purposes) where quality is the imperative, and hasty repairs to return a clashed/cracked/damaged die into service. I'd surmise that two different job classes would perform those operations, judging from the quality of the results.

 

Let me add to the confusion. If I take a flat lap and put extremely course grit on it and then POLISH a die. A coin struck with that abraded die will look like your coin.