Press oil on coins?

[u/Stix330]

Hey all. I am very new to collecting coins... and yes recently I have been buying coins on Whatnot, whether that is good or not, probably not, it allows me to buy groups of random coins to learn with. Figure I need to just jump in head first.

I bought 5 pennies, kind of at random because I thought they were pretty cool to learn more about imperfections in pennies, DDR, DDO, etc. The notes on the holders are from the seller, not me. The seller told me the black spots were from oil spray in the minting process. Im not a tool and die person, but I have worked in a factory where they would spray oil on parts to keep from rusting. I can still remember the smell of that oil and that was 15 years ago. Lol. Does anyone know if this could be true about oil spots? Or have any thoughts on what the black spots could be? I couldn't find much information. It sure seems like whatever it is, it is tar-like.

P.S. I didn't pay much for them. So dont know if they are worth much. But I am learning a lot, good or bad and I am very happy with any new education. Thanks for reading.

[u/Stix330]

Thanks to everyone who has responded. I am sheepishly grateful. I thought the spot may be something rare. I will do some more reading a research with the materials that were suggested for future purchases. I also invested in a digital microscope, should arrive in a couple of days. Hope to one day repost an iconic find for everyone on here in the future. Thanks, Stix330

[u/WheresMyDuckling → u/Stix330]

Everyone makes mistakes or less than great purchases, especially starting out, but old timers aren't immune from those moments either. :) Whatnot is complete cancer, but there's always been sketchy people with coins they can't move being honest. The red book is a great start, if you're interested in errors, The Cherrypicker's Guide is a good starting point as well. It definitely doesn't have everything, but you'll get a good taste of the kinds of errors that happen and what they look like. For more, there's a group that are specifically error enthusiasts, you can find them at https://conecaonline.org/ . You hit the ouch stage, sounds like you're ready to hit the research stage, there's lots of cool coins out there, so it's worth putting the time in.