Impossible To ID Old Coin?

... looks to be the size of a 1700's - 1800's Spanish (milled) 2 reales...(we can safely assume it's not a 2023) ... what is the weight (grams) ?

somebody help this guy with a cleaning idea...

It weighs eight grams and is around 28mm to 29mm in diameter. It looks like a 56 on the front diagonally.

8g is too heavy for a Spanish 2 reales (6.7g), but the encrustation may add weight ...
...28-29mm is the correct diameter for a 17-1800's milled Spanish colonial 2 reale...

...have you checked to see if a magnet will stick? ...

Not everything round and made of metal is a coin. For example, it could be one of those punch-out tabs from an electrical box.

...if it's a punch-out tab, it'll be magnetic ... so, try a magnet ... if it sticks, that rules out any known coin circulating in the original colonies ... because of the size, if it's silver, it'll most likely be European, most common were
Spanish & English ... dang, I love a mystery ...

...you could try reverse-electrolysis to loosten & remove the rust ... if you have access to a car battery charger, you can (fairly) easily do this.

you'll need: 6 or 12 volt battery charger / 2 lengths (2 -3 ft. each) insulated copper wire, (medium gauge) / 2 alligator clips / an old stainless steel utensil to use as an anode / a non-metallic water container such as a 5 gal bucket (plastic) / 10 gal aquarium / plastic bowl (at least 3 gal capacity) / 16 oz. box of baking soda / 2 gals water .

...charger unplugged, attach wires to the + & - leads of the charger, & attach the alligator clips to the other ends of the copper wire. Fill your container with about 2 gallons of water, & mix in the box of baking soda.
..........stir until baking soda is dissolved, then stir some more .......

...attach the positive wire/alligator clip to the utensil (acting as the anode) & place on one side of the container (in the water) ... attach the coin(?) to the negative alligator clip & place in the container on the opposite side, not touching each other, in the water ...

...plug the charger in, turn it on. In a few moments, you wil see a bubbling around the (?)coin, as the process has started. The rust is being pulled away from your (?)coin, & will attach to the utensil( anode) ...

...this process will take days, even weeks, depending on the amount of corrosion ... at least once a day, unplug the charger, remove the items, & stir the water to suspend the settled soda (which provides the electrolytes to the water) ... you may need to replace the water/ soda mixture at some point, if you don't notice bubbling around your (?)coin ...

...be patient, as this is a slow process ... I've done cannon balls & iron objects found in salt water, & been successful, & worth the effort ...

...this is best done outside, but not much fume danger here,so, find a well -ventilated area, where your set-up won't be easily disturbed ...

...keep us posted ...

...your method seems better / simpler, Seeker ... I'd use it instead ...
...My only experience was with salt-water submerged artifacts: cannon balls, anchors, plummets, etc. ... much heavier objects ...
...Here's a 1500's British plummet (depth finder) I found diving in Indian Bay, Delaware ... 400 years of encrustation, took 4 months to desalinate ...