Congrats on your first colonial copper! I know this is gonna sound bad, but it has worked for me as a last ditch effort to get any remaining detail. I had a similar half penny that I couldn't get anything off of. Toothpick, peroxide...nothing worked. I lathered up an SOS pad (soap pad or brillo pad depending on where you're from) and gave it a scrub. Not brutally hard, but moderate. Got enough detail to get a date. Remember, that's only if you're basically Staring at a blank disc once the peroxide ate the verdigris off.