by Dan R. Lynch
Dan R. Lynch has passion for rocks and minerals, developed during a lifetime growing up in his parents' rock shop in Two Harbors, Minnesota. Working with his father, Bob Lynch, a respected veteran of Lake Superior's agate-collecting community, Dan spearheads their series of rock and mineral field guides: definitive guidebooks that help amateurs "decode" the complexities of geology and mineralogy.
Lake Superior agate collecting is a hobby shared by many people in our area. It is also a hobby taken very seriously, and collectors will sometimes do anything to make an agate look better, whether it be cleaning, sawing, or polishing. After growing up in a rock shop that specializes in Lake Superior agates, I’ve seen all manner of evils committed upon agates by collectors, but you can learn from their mistakes. This fall, as the weather grows colder and collecting becomes more difficult, spend the time indoors to care for your discoveries and preserve your collection’s value by following these tips.
A common practice among collectors is using acids to clean agates. I always recommend against this. While acids can yield results, they are dangerous to use, difficult to dispose of, and can actually leach color from an agate when used incorrectly. A much better and safer way to remove stains from agates is to use oven cleaner. Spray your agates with a thin coating of the cleaner (wear gloves!) and place them in a bucket with a tight-fitting lid, then set it in the sun. After the agates have warmed for a few hours, scrub them with a stiff plastic brush in hot soapy water. This will remove surface dirt and staining from your specimen safely, and repeating the process can yield better results.
One of the worst things you can do to an agate, especially a large one, is cutting it when it doesn’t need to be cut. I’m constantly asked if cutting an agate will reveal a more valuable pattern inside. While this can occasionally be the case, more often than not cutting an agate will only cut its value! As a rule, think of an agate as an onion; you can’t see an onion’s layers until it is cut. Agates are the same and show no banding if they are whole. Therefore, if you can see an agate’s banded pattern, nature has already “cut” it open for you, and nine times out of ten, you don’t need to cut it again.
Finally, polishing agates is always a contentious subject. Many serious collectors simply won’t purchase polished agates. Knowing when to polish an agate isn’t easy, but use your best judgment; if an agate already has a beautiful face, don’t polish it. On the other hand, if an agate shows only a little banding but not a full pattern or good coloration, or it is heavily damaged, then polishing may improve the specimen. But in all cases, polishing one side of the agate on a diamond grinder while leaving the backside rough (called “face polishing”) is preferred. Leave tumble-polishing (in which an agate is placed in an automated drum and polished on all sides) for low-quality agates. And if you’re not going to polish your agate but want it to have a shiny, “always wet” look, apply a thin coating of mineral oil.
So use the cold months to give your collection some attention without damaging their beauty--or their resale value!