My ist IHP had a crust that was about 3/16" thick I could not get a date. Iknew it wasn't a zincoln and had ti be an indian head. Since it was my 1st and already toast, I experimented with electrolysis. Left it in a little too long, no harm, no foul.
I've found a couple of IHP's like that too, in a park that used lots of fertilizer. No way to read the date, so, with my luck, they're 1877's or 1869/68's!
Minelab Manticore, Minelab CTX3030 w 11" and 17" DD coils,
Minelab Excalibur II w 10" coil, Equinox 800 (4) w 11" and 15" coils,
Troy Shadow x2 w 7" coil, Pointers; Garrett Carrot, Pro Find 35,