Cleaning coins with electrolysis and results of that with different metal :)

I read a lot about cleaning coins with electrolysis ,and i decide to try.
very very interesting results.

here is experiment coins,i have lot of them :))))))



here is results

2 kopeks 1758 ekaterina material copper

before cleaning.
and after cleaning



10 dinara 1943 serbia - material zinc (picture before cleaning is on group photo)



5 konvertabilni maraka bosnia bi-mettal
before cleaning

and after

3 kopeks 1924 USSR material copper

in middle of process

and finish


1 rouble russia material copper nickel
before

after


and biggest surprise make me the iron Bulgarian coins from 1941,they is been under highly oxidation ,and take a look after cleaning!!!
1,2 and 5 lev 1941 material IRON


what do you think?