Glad you asked! :-) Pre 1982 solid copper cents are preferred by most elongated coin collectors. Post 1982 zinc cents were made of copper plated zinc and can be tricky to clean. Copper plated zinc cents may also show some silver streaking when the thin copper plating is broken. On the other hand, zinc pennies might be preferred if you want to use a coin dated the same year as you pressed it. Plus zinc cents have an advantage when the coin press machine isn't adjusted quite right and solid copper coins are "rolling short". This is because the much softer zinc cents might produce a more complete image or "roll" in the same machine. (As shown in the picture on this page.) NOTE: You may have noticed that coin press machines have different levels of sensitivity to the hardness of the coin being pressed. This is often because the harder copper penny causes coin press machine rollers to "flex" apart more in some machines than in others. That is usually why a new strongly built penny press with rigid coin rollers might not respond to the hardness / softness of a coin as much as a machine with with more flexible rollers. So, results can't be guaranteed. However, given a second try using the tips listed below usually costs only 51 cents, it's probably worth a try. :-)
But wait... Not even all solid copper pre 1982 cents are alike!
Copper cents dated 1980 and 1981 are often "softer" than say 1960s copper cents. So, for a "longer" more complete pressed coin, you might want to try a 1980 or 1981 solid copper cent before you try a softer zinc cent. Don't forget that some machines might press coins longer or shorter depending on the temperature of the machine rollers / coin dies. Lastly, if you are using uncirculated "BU" cents with very clean, dry surfaces, rubbing the coin between your fingers to put just the oil from your fingerprints on it might cause the coin to roll a bit longer. (I know, I didn't used to believe this one either! :-) If that doesn't work, the next tip is a last resort.
How can I make a coin roll a little longer?
Even when using soft coins, like 1980 copper cents or zinc cents, the pressed coin souvenir might still be incomplete or a little "short". This can be disappointing if you traveled a long distance to the coin press location or especially if you paid like $200.00 just to get into the park. In cases like this often long-time penny pressers will carry a tube of Chap-Stick. By just touching your fingers on the lip balm and then rubbing the coin between your fingers, the coin will often magically press longer. Don't use more than just a "finger print" of the Chap-Stick, any more will damage the coin or maybe even make it jam the machine. Not good, especially remembering that you may have driven a long way and paid like $200.00(!) admission... Also, the friendly collector behind you that you were just chatting with in line may have also driven a long way and paid like $200.00(!) admission.
PS Don't forget that some machines might press coins longer or shorter depending on the temperature of the machine, coin dies and rollers.
Any additional tips for pressing nickels, dimes, or quarters?
Pre 1965 dimes and quarters are made of 90% silver and can make for extra nice pressed coin souvenirs, jewelry, and framed sets. "War Nickels" also have some silver in them and it shows when they are polished. Newer nickels, post 2003, are very "flat" not having the relief or 3D look of the early nickels from 1938-2003. However, all nickels with the exception of the "silver" 1942-1945 "War Nickels" seem to press about the same (of course the ghost image left on pressed pre-2003 and earlier nickels is stronger and differs from the image left with post-2003 nickels). Do keep in mind, that these nickel, dime, and quarter coin variations containing silver tend to press "shorter" than their more common nickel, copper, or zinc equivalents and may not fully press in -some- machines. As long time collectors know, some penny press machines, for one reason or another, will produce curved pressed coins. Here is a page with our suggestion of How To Flatten Curved Pressed Pennies.
What if if a coin "skips" in the penny press machine?
Sometimes coins will start late or bounce between the coin dies or rollers because the coin gripper or catch slot is warn or not well implemented. If the coin die's grip slot can't grab the coin, it can't pull it in between the rollers. So, when skipping occurs, it may be worth a try to use a 1963 or 1964 dated cent. The 1963-4 dated cents often have a high, sharp raised edge and may still work. If all else fails, sometimes a machine will have a phone number to request a repair or a nearby cashier may have a spare pressed penny. Related: How to Clean Pressed Pennies and The future of the US Cent. (Yes, maybe too much information. But, this is ParkPennies. It's what we do. :-)
Where can we purchase "Bright Uncirculated" or "BU" (clean, unused) copper cents?
Coin shops and eBay are great places to look. If you are an avid pressed penny collector, you might even want to look for a "Mint Sewn Bag" of 5,000 cents or a "roll" of 50 pre 1982 common date BU cents... maybe a roll of 1963-4's and some 1980-81's? Of course, don't forget about that penny jar at home or the local bank. I know some readers may have one more question...
Is it legal to press pennies in the United States? Yes! Mr. Fowler's letter from the US Treasury established that pressing coins is legal. But, I still want to look around a bit to make sure no one is watching when I press a penny. ;-)