How will you attempt to treat that ?

[leprecoin]

It's Bronze alloy (97% copper, 2.5% tin, and 0.5% zinc)

[HiHoAudio]

99% isopropyl alcohol should lift the goober without damaging the rest of the coin.

 

Maybe...

[BadThad]

VERDI-CARE™ will remove 95% of that in under 5 minutes without affecting the patina. It will require about a 3-4 minute soak and then gently rubbing it with a toothpick for a minute while soaking.

 

The corrosion is fairly deep, there will be a couple of spots remaining after conservation. If you were to remove those you will see some light pitting, so they are best left alone.

[BadThad]

Here is a Lincoln I conserved yesterday. It showed similar corrosion. Total conservation time was under 5 minutes.

[Virtually_Here-migration]

20 ml distilled water with few grains of baking soda followed by acetone bath then xylene also known as xylol and finish with acetone rinse