1622 Spain Maravedis "Cob" Type Question.

http://en.numista.com/catalogue/pieces40542.html

alot of the maravedis where countermarked but not in this case.
and soak it in olive oil for a couple of days to clean it a bit....afterwards a soak in acetone and I'm shure it will already look better

Lanzarote : this place is english only ;)

Ok. Why do so many of these have dirt? Are they found buried?

See here:

http://www.ncbi.nlm.nih.gov/pmc/art.../PMC3342128/

This soil deposit is composed of mineral deposits (i.e., K, Mg, Si, Na, etc - see article). From memory no copper oxide is of this color (i.e., normally green, red, blue, gray, black). So remove it and you remove some coin features as already explained. Even olive oil ...

When running SEM/EDS the analysis normally picks up these common soil metals with an atomic weight less than Sc (At. No.21). We see these all the time on a coin even if cleaned. The two most common contaminants on coins are sulfur and chlorine from the atmosphere. This is why even holding a coin by the edge on a Gem or Proof is still a bad idea as the chlorine from your hand travels from the edge to the surface of a raw coin. No big deal unless your one of those BLAST WHITE accumulators.

However since toned coins are hitting the ROOF with current coin prices they are back in style. Read an interesting article a year or so ago about how toned coins NEED to exhibit a particular range of a rainbow coloration scheme on a silver Morgan for it to be considered original toning. Interesting. Don't have it memorized as I only buy PCGS/NGC Morgans slabbed and usually common ones in MS63+ from the New Orleans Mint only of a two sided tone nature - just personal preference on a rare buying occasion for me anyway within this Federal series. LOL.

JPL