Naval jelly will dissolve the rust, assuming there is enough metal that is
not rusted to retain the integrity of the plate, this might be the best way
to go. The other choice would be rust converter. This chemically changes
the rust into a primer. It goes on clear (from spray can) or milky (liquid
bottle) and in several hours changes to black wherever it contacts rust and
dries to a sandable, paintable surface. It's available (like naval jelly)
in automotive supplies and painting supplies in Kmart, Walmart, and the
like. Great stuff for those rust spots on your car, too.
Wayne Miller

William Maurer writes:

>  Gomez Mill House has restored the root cellar at our site. Dates to around
> 1880. In doing so we dug an additional four feet below what we thought was
> the bottom and found that in our planning we missed another shelf layer. The
> good news is that we found a layer of ash and in that layer enough artifacts
> probably from the owner of the house, Dard Hunter (1912-1918), to keep the
> archaeologist washing and gluing into the late fall.
>
> Questions are: We found a very rusty license plate.  Need the best way to
> remove the rust.
>
> Secondly, if we get a plate number, is there anyway in New York state to
> trace the owner?
>
> Thanks.
>
> Bill Maurer
> Director
> Gomez Mill House
> www.gomez.org