No easy (i.e., inexpensive) way to tell. I have a few 1983-85 set aside that have a distinctive yellow color, which was during the time period that planchet supplier(s?) were having problems with the zinc blanks falling into the plating solution and dissolving. I labeled them as brass on the 2x2s but I can't prove it. You would need to do an elemental analysis like XRF to determine the amount of zinc in the plating and that isn't cheap. Plus, there's a lot of zinc right under the thin plating so there's a possibility that the xray beam will penetrate the surface deep enough to interact. I really don't think the handheld analyzers are sensitive enough to deal with the thin plating. Copper is a very reactive metal so there is always the possibility that the color may be due to other environmental factors, as well. I'm confident that at least 2 or 3 of my coins have a brass coating, but without data, it's just my opinion (and opinions are like certain parts of the human anatomy, everyone has one). Bottom line, it will probably be a couple hundred bucks for a test and unless you really know the equipment and sampling techniques, you can't be sure.
There was an article I read in one of my CONECA magazines written by Ken Potter. He called it a "Yellow Jacket". He was sent one from a coin collector to verify. He had contacted the U.S. Mint and had it confirmed by them that it was in fact a error with the zinc coating solution. It gave the banks a brass color. I found one and just put in a 2 x2 coin holder and filed it away. When I saw the article, I looked up my coin and found it matched up with the article. Ken is an expert on errors. He wrote "Strike it Rich with Pocket Change" and is a content written for all the coin books and magazines. I would do like I did, put it in a coin holder and file it away.
I found another article that answers you question. Go to www.error-ref.com. Then go to the Index of complete entries and look up Brassy Plating. It states the Brassy plating cent are a product of a zinc contamination of within the copper plating bath. The article goes into detail with photos. Really helpful.
Back around 1986 when I started collecting coins. I was filling a Whitman folder of Lincoln cents, and I found in circulation, the two cents on the bottom of the following picture (the top coin is a color reference). I wondered if they came from the mint that way or if the color was post mint. In 2015, while I was searching for information about all the hub changes of the Lincoln cents, I found this reference: From: http://users.scronline.com/lockem/20thcentury.txt This is Mike Locke's best attempt to date at a complete listing of all of the hub design changes to occur in US minor coins (non-gold) of the 20th century. ... .... -1983,1985-D Brass plated zinc Another planchet variety; this one a bit controversial, since the brass color can be simulated by heating a struck coin. Correct coins should be coin brass, the same color as pre 1982 cents; not bright yellow. According to the mint report on these, they should be classified as a mint error rather than a planchet type. The official explanation is that the planchets were overheated during annealing, resulting in zinc migrating into the copper (thankyou, Alan Herbert) Wow, the exact dates and mints I had set aside about 30 years earlier. And I had not set aside any other brassy cents … only these two. It can't be a coincidence, I finally had an answer after all those years. The 1983 was in a Whitman folder all those years, but I put in in a flip after reading the reference. I replaced the 1983 from a jar of cents that I squirreled away that many years ago. I found another slightly brassy 1983 in the jar. It’s not as dramatic as the first two … so I didn’t notice it then. Here is a photo of the second 1983 cent(in a replacement folder) .
I think your answer is the type i would expect on coin talk bravo oldhoopster. Slam dunk. (is that what you call it) Cheech
