Re: what gases are given off during electrolysis?

After consulting my chemistry text and discussing this problem with colleagues, my best educated guess as to what is going on is the following:

1) Citric acid, found in lemon juice, by itself probably dissolves some the crusty material, most likely a copper oxide. The chemical reaction is the following, where HCit = citric acid, CuO = copper oxide, and H2O - water:

2HCit + CuO --> Cu(2+) + H2O + 2Cit(1-)

The (2+) and (1-) indicate a positive 2 and negative 1 charge, respectively. Cu(2+) is now at this point in solution.

2) By applying a voltage, you enable a redox, or reduction-oxidation, to occur. The oxidation occurs with the iron, Fe, in the stainless steel spoon, where e- is an electron:

Fe(metal) --> Fe(2+) + 2e-

3) Now for the reduction. This third part I'm still not completely sure about. Without knowing that gas is given off, I would predict that Cu(2+) found in the solution reduced in the following way:

Cu(2+) + 2e- --> Cu(metal)

The above reaction would result in plating of Cu metal onto the spoon, which you would probably observe after using the spoon several times. Given your observation, however, that a gas is given off, what is more likely happening is the following reduction of hydrogen, H, which comes from the acid as H(1+):

2H(1+) + 2e- --> H2(gas)

Use adequate ventilation, since this gas is extremely flammable (I presume from your question that it has no odor). But do not worry too much, as the gas quickly mixes with the air above your container. Keep open flame away from your container, to be extra safe.

As far as the comparison in vigor to ferrous substances, the rate of gas coming off is directly related to the reaction rate, and could even be related to the dissolution rate of your oxide material. So, if the Fe oxide dissolves more quickly than Cu oxide in citric acid, this could in turn produce a faster evolution of gas. Best of luck with the artifacts.