1812 Capped Bust Half Dollar (Large 8?)

First of all, do not clean the coin! It is quite possible to irreparably damage the coin in the process. Second of all, larger pics will be needed to properly attribute the coin. If you do indeed have the Large 8 variety(which is quite a valuable coin), that coin will need some professional conservation to remove the rust staining. NCS is the best company to do that, they have conserved the National Numismatic Collection at the Smithsonian so that should give you an idea how well they are regarded.

Welcome to Coin Community, plusbryan. It should be noted that the "Large 8" variety which carries so much additional value is the 1812/11 overdate, O-101; most other varieties of this year also have an 8 which is larger than the adjacent numbers.

The actual overdate feature of O-101 can be difficult to see; it's best to aid the attribution by noting a much larger space between the 1 and 2 than the other numbers. Another good identifying feature, and one which makes me certain that your coin is not O-101, is where the M in UNUM locates relative to the A in STATES. With O-101, the right side of the M is directly below the space between the serifs of the A; your coin has the M placed too far right.

It should be a millimeter or so larger than a Kennedy half.

Although I'm not necessarily opposed to the average collector learning safe methods of conserving his coins, the residue on the reverse of this one is probably best left to professionals, so I would agree with biokemist's recommendation that the coin be submitted to NCS if conservation is desired. Note that the cost of this process will rather eat into the potential profit value of the coin, though.

Not for long.

Just because it isn't O-101 doesn't mean it lacks value. The stuff on the reverse is obviously a dealbreaker for value, but it's easily a $100+ coin if it can be safely removed. It looks like something was allowed to sit on it while rusting. Silver doesn't "rust," so it might be a good candidate for NCS conservation.

Here's how it works: You have to be a member of NGC/NCS to submit to them directly; in your case you'd want to find a local dealer who can submit on your behalf. NCS gets the coin and evaluates it. That'll cost you $5. If they don't think they can help, they send it back and that's it.

If they think they can help, you're out another $15 for the service. You can then (optionally) ask them to either encapsulate it themselves, if it is still a "problem" coin which can't be graded by the usual process, or they can submit it to NGC (their co-company), who will encapsulate the coin with a numerical grade. This will cost another $15-20.

My quick guess from the photos is that this is a VF35-XF40 coin. It's worth $125-125 in an NCS "XF Details" slab, and $200-ish in an NGC XF40 slab. With that said, I'm stretching to make conclusions based on such small photos; I do so because the wing and hair details look really good even in these small shots. With better photographs, my opinion might change.