The copper electrodes from any zapper can turn black. However, it is recommended that the copper should be covered with a good paper towel soaked in salt water to keep the copper off of the skin, increase conductivity, increase effectiveness, and reduce the risk of burns. Can't do that with the terminator types.
Some things to know about zapping:
The larger the contacts ( up to a reasonable point ) the greater the conductivity and generally the better the results.
The further apart the contacts are, the better the results ( as long as they maintain contact ).
More contacts ( up to a reasonable limit ) will improve results. Four is a good number, but it is important to understand that there should be only one ground or negative contact. The best combination that I have found is 3 positive and 1 negative, with 1 at each extremity.
Always keep the metal off of the skin by using a paper towel or disposable cloth. Soak either in water, using salt water increases conductivity.
If you use copper paddles and footpads in augmentation mode ( 3 positive and 1 negative ), it is effective enough that it may destroy a lot of the intestinal flora. As a result, it is important to take a good source of probiotics after zapping. This is strong evidence that zapping can reach the interior of the body. BTW, I prefer a good yogurt or kefir over the pills.
This is only a small part of the information that is provided in "Parasite Zapping and the Zapper", an 80 page booklet which costs $12.95 from http://paradevices.com
The booklet tells you a lot about how to get the best results when zapping and also what not to do.