Right out of the hole, I almost always spray the dirt off of any silver coins with a water/alcohol mix in a small spray bottle I carry. It helps eliminate the possibility of scratches from wiping the dirt off with my fingers, etc. Once I get home, I clean each silver with regular dish soap and running water to get rid of any remaining dirt and grime, first using gentle rubbing with my fingers, and then using a very soft bristled to get dirt out of all the crevices. For some coins, that’s all that I need to do to get them looking nice.
For the Seated Liberty dime in this case, there was still a lot of black oxidation in uneven splotches left on the coin after the soap and water bath which doesn’t look good in my opinion, and hides detail. The Trime barely looked touched by the soap and water bath. So I moved to the next step…science! Baking soda, aluminum, and hot water are your best friend for cleaning silver:
For the details on why it works, check out this website:
http://blog.teachersource.com/2014/01/18/chemistry-of-tarnished-silver/
For the Seated dime, I only needed to repeat the process two or three times, and it worked very well. For the Trime, I lost count how many times I repeated the process. In fact, I finally needed to resort to going a little harsher and manually rubbing in a weak baking soda/water paste in between the last few hot water/aluminum/baking soda reaction treatments. The baking soda paste step is less desirable, because while the coin will look good to the naked eye, mild magnification will reveal the scratches left by the abrasive action of the baking soda…and like any polish, some silver is removed in the process in general.
For Rosies and non-keydate Mercs, I sometimes just go right to using a baking soda/water paste after the soap/water bath - takes care of the oxidation very quickly and gives the coin a shine like it originally came out of the mint to the naked eye. The method (or any cleaning period) is unacceptable to some, but to me, the coins look far better cleaned this way than the uneven oxidation they have from being buried for decades, which ruins their numismatic value anyway. I’m not looking to sell the coins, just preserve their overall condition for posterity, so I clean them guilt free.
I’ll definitely be back to the location…might even try your old 15” coil there. Finding that sash buckle-like item as deep as it was got me wondering if a big coil might bring some other items into range. 
Seriously, I’ll be amazed if I see another one under my coil the rest of my detecting days, but it’ll sure be fun trying!major congrats on so many awesome finds! Downright amazing finds!
